Christopher Nolan was purportedly the reason it didn't make it in—and it was no longer a problem by the time the Joker sequel was coming around.
Joker: Folie à Deux’s Ending Came From a Scrapped Idea for the First Film
Christopher Nolan was purportedly the reason it didn't make it in—and it was no longer a problem by the time the Joker sequel was coming around.