Season 1s are great, setup, some payoff, a bit of lead into the overarching story. Then season 2 to X. The heroes win and then lose in the final episode, cliffhanger to next season. People get bored. Final season is announced and they wrap up the show.
Ultimately, the primary satisfaction of storytelling comes from the story ending.
You can do that episode to episode, season to season, etc. I feel like the best shows balance by having plot archs and character archs that can happen independently of each other. That way each episode or two can close one kind of arch while opening another. Because they are different kinds of problems, they’re less likely to conflict, giving you the sense of closure you crave while also creating a sort of cliffhanger.
That’s really hard to do well though, especially over time. And usually expensive.
A lot of shows start with 2-3 seasons of concepts in mind, and hope to get picked up for more. At that point it gets exponentially harder to go on without detracting from what you’ve already built.
I’m glad that most streaming platforms are starting to see value in shows with a fixed ending in mind, it just makes for better storytelling.