Well, I'd say that the standard movie format just isn't what people want anymore.
The problem movies have is they have a relatively short amount of time to deliver a complete story. 90 to 120 minutes just isn't a lot of time to be compelling. That's why some of the best movies are split into parts.
Consider Andor as an example. It's some of the best media ever made (IMO) and it simply would not work in the movie format. What makes Andor work is the excellent character development and the time spent building and shaping the universe under a fascist government.
Andor had no length constraints per episode. That allowed it to tell complete satisfying stories with the promise that you'll get more in the next episode.