Bottle episodes meant people didn't need to be invested in years long sagas. People don't know what they want. They're force fed fancy wine, thinking they've become connoisseurs by their own choice, but actually it's box wine from Walmart. They get fed up and quit after a season or two, but they don't know why. They tell themselves it's because the writers or studios are doing it wrong. Of course that's true, but not for the reasons they think. Give people something easier to digest in small bites and they'll continue watching shows.
The same problem happened to Marvel. At this point nobody has kept track of the dozens of movies and all the plot lines. They lose viewers by attrition. They gain none because nobody is watching hundreds of hours of movies to catch up. Bottle episodes and standalones make it easy for people to start and stop at any point.
Standalone content got a derogatory label "filler". So people hate it because they're told to.
