According to Quora (https://www.quora.com/Why-was-the-television-sitcom-Three-s-Company-cancelled-in-1984-Do-you-think-an-updated-version-of-this-show-would-be-popular-today/answer/Jon-Mixon-1):

Low ratings and it ran out of story.

When Three’s Company started it was a pale imitation of the British series A Man About the House. Its premise was slender (A guy pretends to be gay so that he can live in a cheap apartment with two young women) and it simply never grew sturdier. What allowed the program to succeed in the first four seasons was the character interplay between the star John Ritter, his two roommates Joyce DeWitt and especially Suzanne Sommers; and their first landlords, The Ropers, portrayed by Norman Fell and Audra Lindley.

Unfortunately as time went on:


The Ropers were spunoff into their own series that failed. The contract both performers signed would have allowed them to return to Three’s Company had the new series failed in its first season. It managed to get two seasons and so they were “out”.
They were replaced by comedy veteran Don Knotts who tolerable as Ralph Furley, the new building owner. Unfortunately while Knotts was always a trouper, other than leer at women and make snide ‘jokes’ about Jack’s faux-homosexuality, there wasn’t much for him to do and things never got better for him.
Suzanne Sommers and her husband, who was also her agent, realized that the series depended upon her as much as it did John Ritter, the lead. They entered into negotiations with ABC which went poorly. The network slowly began to transition Sommers away from the show and then fired her after the end of the fourth season. She was “replaced” by two other blonde actors, neither of whom gelled with audiences.
Ritter became the focus of the series, but unfortunately his pratfalls and “misunderstandings” with his female roommates were both growing stale. Joyce DeWitt unfortunately wasn’t much help as her character was written so poorly she began to disappear into the background behind the new blondes, Furley, and even Richard Kline (Larry) who portrayed the smarmy used car salesman who lived upstairs, and who was promoted to the main cast in the fifth season.
Finally, the series dropped any pretense of Jack and his various roommates ever having any sexual encounters and gave him a girlfriend, who brought a sitcom veteran actor named Robert Mandan with her to somehow bulk up the scripts. Unfortunately for them, the ship was already sinking at that point and there was nothing that could be done to save it. By the eighth season, ratings plunged and the emphasis was on a spinoff for Jack that took him away from the apartment setting and didn’t include his soon to be former castmates as anything other than guests.
Soooo…. Three’s Company was canceled because its ratings plunged, it was no longer “winning” its timeslot, and because the production and the network wanted to move ahead with the spinoff series Three’s A Crowd, which unfortunately for all involved barely lasted a season before being canceled itself.


Could a series like it work today?

No.

Why?


It was surprisingly homophobic
It was quite sexist
Its core premise was absurd even for the time.
There are simply too many other sitcom options available on networks and streaming to make it viable.
Three’s Company was a product of its time…and times have changed.

and it was funny and today's sitcoms aren't. They're nothing but trash.

It was never cancelled it was revamped and changed into a new show

Hands down the funniest show ever (take that Seinfeld), I discovered the show in syndication so I was unaware of the backstage drama till years later. The changing of landlords and roommates leaving I just assumed was a natural progression of the show.

The show for me is never tiresome, John Ritter and his gift for comedic timing was the glue that kept the show afloat.

Ratings.
Three's Company was constantly in the top 10 and even in the top 3 in its prime. By the last season in 1984, Threes Company fell to #33. It was stale and outlived its original premise. In 1977, 3 roommates live together in a 2 bedroom apartment for the purpose of sharing the rent. By 1984, Jack had his own restaurant, Terri was an emergency room nurse, and Janet was manager of a Flower Shop. There was no need to pull together to share a small apartment. In 1977 it was scandalous for a guy to live with 2 women. By 1984 it was not unusual. The last season had recycled scripts too. It stayed on 2 seasons too long IMHO.
In my heart, All In The Family will always be the best sitcom. But Threes Company is a close #2. I watch it almost every day and have seen every episode hundreds of times and I still laugh out loud. I know the joke is coming but its delivered so good I still laugh. The Older Woman is my favorite episode. It has the perfect mix of the roommates, sexual innuendo, the Ropers, and a fall out of the chair laughing Larry scene.

#33 ranked show is considered good enough for renewal for some shows but I guess expectations was higher for TAC with John Ritter

It was never cancelled it was revamped and changed into a new show

I remember reading John Ritter said Three's Company was cancelled. The network didn't want another season of the show because the ratings declined too much.

Producers offered the network a "replacement" show for it. He said if he didn't do Three's A Crowd, there still wouldn't be another season of Three's Company.

Did the creators of Three's a Crowd really expect the show to meet or surpass the last season's ratings of Three's Company?

I always thought that TAC was created as a way to have a smaller budgeted sitcom. It's as if the show went from a triple meat Whopper sandwich to a kids meal cheeseburger. I think most of the $$$ went to John Ritter, the obvious star, but then they had limited guest stars or even day actor/actresses.

Looking back, it was a strange thing to do for fans of the show.

The success of TC was based on perfect and unique comedy show at the right time. Can never be duplicated. Came in when ABC comedies dominated ratings. It was in right place at right time. The idea was ground breaking and perfect star in Ritter with A plus supporting cast. In hinds sight, the network was smart to let Sommers walk away, or in her case fired. They had 2 more seasons of top 8 ratings, with it being top rated ABC comedy seasons 6 and 7. Although being politically incorrect, 3 networks only helped as well. In 2 days world of TV, cable, Netflix, etc it would have never survived. Different culture and life in 2023 than 1977.

The success of TC was based on perfect and unique comedy show at the right time. Can never be duplicated. Came in when ABC comedies dominated ratings. It was in right place at right time. The idea was ground breaking and perfect star in Ritter with A plus supporting cast. In hinds sight, the network was smart to let Sommers walk away, or in her case fired. They had 2 more seasons of top 8 ratings, with it being top rated ABC comedy seasons 6 and 7. Although being politically incorrect, 3 networks only helped as well. In 2 days world of TV, cable, Netflix, etc it would have never survived. Different culture and life in 2023 than 1977.

How dont know how any network tv show survive in the Internet/Streaming era

The success of TC was based on perfect and unique comedy show at the right time. Can never be duplicated. Came in when ABC comedies dominated ratings. It was in right place at right time. The idea was ground breaking and perfect star in Ritter with A plus supporting cast. In hinds sight, the network was smart to let Sommers walk away, or in her case fired. They had 2 more seasons of top 8 ratings, with it being top rated ABC comedy seasons 6 and 7. Although being politically incorrect, 3 networks only helped as well. In 2 days world of TV, cable, Netflix, etc it would have never survived. Different culture and life in 2023 than 1977.

I agree with you that it came in at the right time with the perfect cast. With that being said, I think it would still work in 2023. The main reason being... it was funny!

If a show is good (which is rare nowadays), the word of mouth spreads faster in this day in age of social media. The really good shows are thriving, and the bad ones (and there are many) don't survive.

It was never cancelled it was revamped and changed into a new show

Admittedly, by the eighth season (https://jacksonupperco.com/2015/07/28/the-ten-best-threes-company-episodes-of-season-eight/) (1983-84), it was probably the "right" time to end Three's Company. Given that Jack now owned his own his own restaurant, which had a room upstairs, it was probably no longer "realistic" or plausible for him to still need to live with Janet and Terri.

Admittedly, by the eighth season (https://jacksonupperco.com/2015/07/28/the-ten-best-threes-company-episodes-of-season-eight/) (1983-84), it was probably the "right" time to end Three's Company. Given that Jack now owned his own his own restaurant, which had a room upstairs, it was probably no longer "realistic" or plausible for him to still need to live with Janet and Terri.

Yes after the restaurant his focus should have been moving out to be on his own since he was making more money

Did the creators of Three's a Crowd really expect the show to meet or surpass the last season's ratings of Three's Company?

I always thought that TAC was created as a way to have a smaller budgeted sitcom. It's as if the show went from a triple meat Whopper sandwich to a kids meal cheeseburger. I think most of the $$$ went to John Ritter, the obvious star, but then they had limited guest stars or even day actor/actresses.

Looking back, it was a strange thing to do for fans of the show.

Perhaps the thinking or reasoning behind Three's a Crowd is that as long as they kept John Ritter front and center, the rest of the cast was in essence, replaceable. I mean, Three's Company had to deal with several cast shake-ups at yet, it remained popular. And by the time that Priscilla Barnes showed up in the sixth season (https://jacksonupperco.com/2015/07/14/the-ten-best-threes-company-episodes-of-season-six/), it probably wasn't too subtle that Three's Company was really a John Ritter starring vehicle instead of an even-handed ensemble show.

Yes after the restaurant his focus should have been moving out to be on his own since he was making more money

Somebody probably hit the nail on the head when they said (https://www.datalounge.com/thread/22591202-priscilla-barnes-on-three-s-company-) that when (http://boomerbust-scooter63.blogspot.com/2013/06/seventies-sitcoms-1976-1977.html) Three's Company (https://nikdirga.com/2024/03/01/a-gay-old-time-revisiting-threes-company-in-a-changing-world/) started back in 1977 (https://jacksonupperco.com/2015/06/16/the-twelve-best-threes-company-episodes-of-seasons-one-two/), with a real '70s ethos (http://boomerbust-scooter63.blogspot.com/2013/07/seventies-sitcoms-1977-1978-raunch.html). It was show about three young people who were having what were traditionally young people's adventures: finding their way in life and work, dating/sex, worries about money.

By the time (https://www.quora.com/What-caused-the-difference-between-70s-sitcoms-and-80s-sitcoms-70s-sitcoms-like-All-in-the-Family-Maude-Sanford-Son-and-Good-Time-were-more-daring-and-confrontational-But-80s-sitcoms-like-Webster-or-Full-House-were) that it ended in 1984 (https://jacksonupperco.com/2015/07/28/the-ten-best-threes-company-episodes-of-season-eight/), we were smack dab in the middle (https://books.google.com/books?id=ZstEDwAAQBAJ&pg=PT76&lpg=PT76&dq=three%27s+company+ended+during+reagan+era&source=bl&ots=B-VqkOHekj&sig=ACfU3U2nkjmAZZzHyCQLPkUyNWsQHXjhvg&hl=en&sa=X&ved=2ahUKEwin0-egjbeFAxUuSDABHYZYC1I4FBDoAXoECAIQAw#v=onepage&q=three's%20company%20ended%20during%20reagan%20era&f=false) of the Reagan-era and Jack, Janet, and Terri were presumably well in their 30s. And it goes without saying that it was bound to be less funny and less physical, because by then, people like them were typically more settled: married with a kid, steady job, etc. rather than living with two roommates in Santa Monica. There probably weren't as many good opportunities for misunderstandings (http://boomerbust-scooter63.blogspot.com/2013/09/onward-seventies-sitcoms-into-eighties.html) or double entendres (https://www.avclub.com/three-s-company-pushed-the-limits-of-double-entendres-o-1798259407) in other words if Jack had the Bistro, Janet was in the flower shop, and Terri was at the hospital.

It was never cancelled it was revamped and changed into a new show

I guess in that regard, that would be like saying that All in the Family never really got canceled, it was just revamped and changed into Archie Bunker's Place.

Ratings.
Three's Company was constantly in the top 10 and even in the top 3 in its prime. By the last season in 1984, Threes Company fell to #33. It was stale and outlived its original premise. In 1977, 3 roommates live together in a 2 bedroom apartment for the purpose of sharing the rent. By 1984, Jack had his own restaurant, Terri was an emergency room nurse, and Janet was manager of a Flower Shop. There was no need to pull together to share a small apartment. In 1977 it was scandalous for a guy to live with 2 women. By 1984 it was not unusual. The last season had recycled scripts too. It stayed on 2 seasons too long IMHO.
In my heart, All In The Family will always be the best sitcom. But Threes Company is a close #2. I watch it almost every day and have seen every episode hundreds of times and I still laugh out loud. I know the joke is coming but its delivered so good I still laugh. The Older Woman is my favorite episode. It has the perfect mix of the roommates, sexual innuendo, the Ropers, and a fall out of the chair laughing Larry scene.

The American sitcom format was already in a tough spot (https://www.quora.com/How-did-the-sitcom-format-become-dead-in-the-early-to-mid-80s/answer/Joe-Roberts-41) by 1982-83 (https://www.sitcomsonline.com/boards/showthread.php?t=146509) (which would've been Three's Company's (https://jacksonupperco.com/2015/07/21/the-ten-best-threes-company-episodes-of-season-seven/) 7th season (https://www.dvdtalk.com/reviews/review/23059)). Only two half hour sitcoms were in the top ten in the Nielsen ratings (https://en.wikipedia.org/wiki/Top-rated_United_States_television_programs_of_1982%E2%80%9383) that year, M*A*S*H, which in no small part, was likely helped by the Super Bowl level type numbers that its finale (https://en.wikipedia.org/wiki/Goodbye,_Farewell_and_Amen) received, and Three's Company (https://jacksonupperco.com/2015/07/21/the-ten-best-threes-company-episodes-of-season-seven/), which was ranked #6. The rest were hour long dramas like Dallas, Magnum, P.I., and Dynasty, with the news magazine show, 60 Minutes having the top rated spot.

The success of TC was based on perfect and unique comedy show at the right time. Can never be duplicated. Came in when ABC comedies dominated ratings. It was in right place at right time. The idea was ground breaking and perfect star in Ritter with A plus supporting cast. In hinds sight, the network was smart to let Sommers walk away, or in her case fired. They had 2 more seasons of top 8 ratings, with it being top rated ABC comedy seasons 6 and 7. Although being politically incorrect, 3 networks only helped as well. In 2 days world of TV, cable, Netflix, etc it would have never survived. Different culture and life in 2023 than 1977.

This review (https://www.dvdtalk.com/reviews/review/24326) probably better explains it:
There's a reason Three's Company was so successful: it was a good show, made funnier with terrific performances by John Ritter and the rest of the cast...but it was certainly more than the sum of its parts. Though it was never really a staple of mine growing up (even in syndication), it's a fun, light-hearted diversion that seems to have held up surprisingly well in the last 25-odd years. Three's Company's reliance on sticky situations was hardly anything new (especially by sitcom standards), but the risqué double entrendres really pushed the envelope back then---and who knows, it might even raise a few eyebrows in today's world of PC television. Either way, Three's Company really clicked with audiences and has maintained a strong following over the last few decades. It may not be in the same league as I Love Lucy or The Honeymooners (or is it?), but it's a fine example of a sitcom that proved to have real staying power.

I guess in that regard, that would be like saying that All in the Family never really got canceled, it was just revamped and changed into Archie Bunker's Place.

Yes it was a continuation

I guess in that regard, that would be like saying that All in the Family never really got canceled, it was just revamped and changed into Archie Bunker's Place.

I see it that way, too. The same goes for The Golden Girls becoming The Golden Palace, and The Andy Griffith Show becoming Mayberry R.F.D..

Yes it was a continuation

Agreed.

I see it that way, too. The same goes for The Golden Girls becoming The Golden Palace, and The Andy Griffith Show becoming Mayberry R.F.D..

The Golden Girls became The Golden Palace because Bea Arthur left the show.

The Andy Griffith show became Mayberry R.F.D is because Andy Griffith left the show (it was #1 at the time).

Three's Company ratings fell of the cliff in season 8. There wasn't going to be a season 9. It was a completely different situation than those other shows.

The recycled scripts and John phoning in some of his performances didn't help.