There’s never going to be a satisfying “real reason” to things like this. The reality is probably something fairly unremarkable like them not getting along and they can’t talk about it because of an NDA or because they want to be polite, especially following his death, people generally don’t want to speak ill of the dead. Much less say something that makes it sound like they were mean to someone who folks view as a martyr.

Pretty much every professional “break up” works out like this. Folks who are curious about it assume there was something bigger going on or something malicious. That’s rarely the case.