Because the characters.
BvS came out with a depressed as hell murdering Batman. Why should I give a f bout him? Superman was depressed as hell didn't know what to do with his life. Why should I care about him? Who's even looking forward to seeing these characters in the next Justice League movie? Are people going to cheer when they see Superman back?
The reason why MCU movies get a pass is because the audience is in love with the characters. Marvel took it's time and sure the plots have been mediocre, but the characters have grown with the audience in every movie. The characters are what makes the MCU, not the plots. Take Tony Stark, going from a selfish prick to now mentoring Spider-Man due to the trauma and the selfish mistakes he's gone through in all the movies.
If you don't care about any of the MCU characters then obviously you are going to hate the movies. But what you need to realize is, this opinion is in the minority and you just need to accept it and move on or stop watching the movies all together, while people like me will enjoy the ride while it lasts.
We are watching the next movie to watch the next adventure of these characters not for studying art or how to make a time tested movie.
Fox is gonna make a Dark Phoenix movie and I don't give a crap about any of the young characters other than Quicksilver. Why would it affect me that Jean became evil now?