Granted, Three's Company was still, a top ten rated show, but in Season 5, it dropped to eighth place (http://www.thetvratingsguide.com/1985/03/1980-81-tv-ratings.html) after being the #2 rated show for the prior two seasons. And then the following year (Priscilla Barnes' first season), the ratings improved as the show finished in fourth place (http://www.thetvratingsguide.com/2020/02/1981-82-ratings-history.html) for the season. Season 5 is the worst rated season other than the first one (which finished in 11th place (https://tvaholics.blogspot.com/2013/03/classic-tv-ratings-and-rankings-1976-77.html)) and the final one, which dropped all the way to 33rd (http://www.thetvratingsguide.com/2020/03/1983-84-ratings-history.html) in the Nielsen ratings.

By season 5 some of the magic was gone and the show was getting stale. With Suzanne gone many thought the show was coming to an end. Season 5 gets a bad rap but there are some great episodes there before Cindy and with Cindy. The Ropers got cancelled and it felt like Threes Company could be next. The show was already in transition with the Ropers leaving and then Suzanne left. The turmoil impacted the quality of the show no doubt.

Granted, Three's Company was still, a top ten rated show, but in Season 5, it dropped to eighth place (http://www.thetvratingsguide.com/1985/03/1980-81-tv-ratings.html) after being the #2 rated show for the prior two seasons. And then the following year (Priscilla Barnes' first season), the ratings improved as the show finished in fourth place (http://www.thetvratingsguide.com/2020/02/1981-82-ratings-history.html) for the season. Season 5 is the worst rated season other than the first one (which finished in 11th place (https://tvaholics.blogspot.com/2013/03/classic-tv-ratings-and-rankings-1976-77.html)) and the final one, which dropped all the way to 33rd (http://www.thetvratingsguide.com/2020/03/1983-84-ratings-history.html) in the Nielsen ratings.

Season 5 is when Suzanne Somers left the show. Also...

1) Some of her fans stopped watching so the ratings went down a little.
2) During that year, the show was getting bad press too. Suzanne and her husband was on talk shows trashing the producers.
3) People wanted to see Jack. Janet, and Chrissy... not Cindy.

By the time season 6 came around, Suzanne was already long gone and Priscilla was everywhere promoting the show. People were curious about the "new girl".

On the True Hollywood Story of Threes Company they claim the ratings drop was due to the less frequent sexual innuendo in the scripts. The producers felt Cindy was too young to be put in those situations which is why she was axed. With Terri they were able to go back to the sexual themes right away like when Terri thinks Jack is working as a gigolo and charging $25.
I necessarily don't agree with that but this is what the executives at ABC thought.

I don't think this factor made to much of a difference in the ratings, but Season 5 started later because of a writer's strike. It was the 2nd shortest season, after Season 1.

On one hand, I was glad Chrissy was gone because her stupidity was ruining the show. But on the other hand, there was no closure for the Chrissy character. The public drama offscreen would be the reason for any ratings drop.

There was a honeymoon period when Terri came on, but it didn't take long for TC to start recycling strips.

The irony is that the two characters that get bashed the most, Chrissy & Cindy, were long gone by season eight.

I don't think this factor made to much of a difference in the ratings, but Season 5 started later because of a writer's strike. It was the 2nd shortest season, after Season 1.

On one hand, I was glad Chrissy was gone because her stupidity was ruining the show. But on the other hand, there was no closure for the Chrissy character. The public drama offscreen would be the reason for any ratings drop.

There was a honeymoon period when Terri came on, but it didn't take long for TC to start recycling strips.

The irony is that the two characters that get bashed the most, Chrissy & Cindy, were long gone by season eight.
Those are excellent points.
Season 5 is so sporadic. It begins with Chrissy. Then Chrissy is missing and away at her mom's. Then Cindy shows up. Then Chrissy shows up at the end with phone calls. We even get the Ropers for a return.
There is a little bit of everything in season 5.

Those are excellent points.
Season 5 is so sporadic. It begins with Chrissy. Then Chrissy is missing and away at her mom's. Then Cindy shows up. Then Chrissy shows up at the end with phone calls. We even get the Ropers for a return.
There is a little bit of everything in season 5.

Agreed, all points well taken.

I don't think this factor made to much of a difference in the ratings, but Season 5 started later because of a writer's strike. It was the 2nd shortest season, after Season 1.

On one hand, I was glad Chrissy was gone because her stupidity was ruining the show. But on the other hand, there was no closure for the Chrissy character. The public drama offscreen would be the reason for any ratings drop.

There was a honeymoon period when Terri came on, but it didn't take long for TC to start recycling strips.

The irony is that the two characters that get bashed the most, Chrissy & Cindy, were long gone by season eight.

I wonder if the ratings went up during Season 6 because of the mere curiosity factor regarding how Terri was going to fit in. Season 6 (https://jacksonupperco.com/2015/07/14/the-ten-best-threes-company-episodes-of-season-six/) incidentally, is I believe, generally considered to be (https://sitcomsonline.com/boards/showthread.php?t=462198) the best among the three seasons with Terri.

Most logical answer is Somers departure from the show after she was fired in 1981 and I’m currently binge watching the show and wondering what seasons 5-8 are like.