It's probably just a calculated decision in the end. If Depp stays with the filmmakers, he puts their reputation in jeopardy. If nothing else he doesn't seem to be the kind of person who wants others dragged up in his own messes, so whether he wanted to spare the filmmakers that horror, or whether he was not really given a choice but to leave, not surprised to see him just leave instead of raise a huge stink and drama on them. (And whoever may be hounding the studio over this now is missing the point entirely)