https://tvline.com/2019/07/23/shorter-tv-seasons-better-13-episodes-fewer/

"As recently as 10 years ago, it was almost unheard of — and certainly atypical — for a TV show to deliver fewer than 22 episodes in a season," says Matt Webb Mitovich. "But now? People seem to be OK with, if not outright embracing, markedly shorter seasons. Is that because there is so much TV to consume, or because we value, as the saying goes, 'Quality over quantity'? Why is less now more?" Mitovich adds: "In the past year or so, we seem to have entered a new phase of acceptance. A phase where Lucifer being 'saved' with just 10 episodes ultimately proves to be heavenly. Where, regardless your opinion of the outcome, Veronica Mars‘ eight-episode rival proved perfectly bingeable. We waited a small eternity for the third batch of Stranger Things, and yet its eight-episode length was no less than satisfying — and not a casualty of the infamous 'Netflix bloat' that tended to make the streamer’s Marvel shows a slog."

The Sopranos

I think it is due to a combination of factors: including the popularity of cable shows like The Sopranos, Mad Men and Breaking Bad which typically had shorter seasons than broadcast network series. Also the rise in popularity of streaming series like Orange Is the New Black or Black Mirror which also usually have shorter seasons. And lastly, the fact that there is just too much TV to consume and people are living busier lives than they did 10 years ago. We work longer hours; many people of the younger generation have 2 or 3 jobs and not as much free time.

Also, I think the driving force behind this has been the industry itself. Actors don't want to commit six years of their lives to making 24 episodes a year; when they can work on a streaming or cable show making 10 episodes a year for 1-2 years. This is why you see a lot of marquee talent at HBO, Netflix and Hulu and fewer big names on ABC, CBS, NBC, FOX or The CW.