Decided to double check, and it appears
Scorsese gave a pretty clear reason for why he decided to not be a part of Joker. He played the "I just didn't have time" card at first, but then said fuck it and told the interviewer what he really thought. He really and truly wants nothing to do with comic book movies. Not even a little. He clearly resents the hell out of them.
He was
reportedly interested in telling Arthur's story. He just didn't want to take that final step and have Arthur's arc end with him becoming a comic book villain, an "abstraction." That was a line he couldn't cross.
I thought it was comic book
movies that he hated. Evidently, his disdain for "theme park movies" (aka "not cinema") includes simply having the protagonist of a "real movie" become a
realistic version of a comic book character, even if the film itself has *next to no* comic book movie elements or hokie comic book villain hijinks.
I say "next to no" because, as much as I love how grounded and believable Joker is, I readily admit the
next-to-last scene kinda sorta veers into comic book movie territory. Not enough to turn Joker into a comic book
movie, imo. But that specific scene is definitely more outrageous than everything before it. Thankfully, it's so god damn phenomenal, no one but Scorsese would say it shouldn't be included in the film.
My dude is bitter and petty with this anti- super hero shit.
I do understand why he's upset, though. He explains that well enough, and I agree with him to a point. It's just a shame such an accomplished and highly regarded legend of the industry chooses to obscure a valid complaint by expressing it in such a snobby and elitist way. I'd expect that of someone like myself, but it seems like an all time great storyteller like Marty could get his point across without being snooty.