When Pick discusses leaving DS, it's usually it was getting too loud, he didn't want to be pidgeonholed, wanted more freedom explore other venues, didn't want to be away from his family, etc. He also says there are other issues that he doesn't want go into.
In the RHoF interview, it's clear that he's not on good terms with neither Mark, John nor David. Makes me pretty sad that almost 40 years later these guys have not reconciled. I was in touch with Pick's wife some time ago, and she basically said Mark and Pick hadn't spoken to each other since Pick left ...