With out a doubt I think the majority are leaving or been forced to leave because of immorality.
Of course once you realize the religion is a false construct of delusional humans you also understand that concepts such as "immorality" are part of the contrived belief system.
Ultimately, whatever the reason a person leaves or is "kicked-out" it's because they do not share the groupthink delusion of the cult.
A cult has to demonize such individuals to maintain their fragile beliefs and keep control.