This is why WB sucks so much at making a cinematic universe. They set all the movies AFTER all the key plot points, and interesting stories that would make good movies.
I mean wouldn't it be more meaningful to actually show what went so wrong in Batman's life and show Joker before he got busted up for whatever he did to Robin?
But no, the audience isn't good enough to have good movies that connect with each other in interesting ways.
All they get is a mess of shit, that range from mediocre to horrible.