With the whole superhero stuff it’s also a consequence of their own success. Back in the day there weren’t many super hero movies, so we watched them even though they were campy and mediocre (batnipples come to mind).
Then they had some real bangers mixed in with trash and the whole thing took off. The Dark Knight trilogy for example and the first Iron man movie, just to name some. People have then come to expect that level of quality, while most of what they put out is mediocre and a lot of it is total trash.
Instead of working on quality they worked on quantity, riding the wave as hard as they could. But people only give it so much chances, there need to be some good movies to keep on coming back. Instead the quality declined and went back to mediocre/trash levels, but since people remember the good ones it’s not acceptable anymore.