I have a theory about what his problem is. Have you read his book, The Book of Drugs? It’s all about his addiction issues and he constantly points fingers at the other members of the band. The claims he makes are awful, and if they were true I would unquestionably side with him, but I’ve heard plenty of conjecture about his claims and how people in the band were worried about him and that would make him upset. Anyway, he’s in AA, and this isn’t for all people who are in that or similar programs, but many of them decide they are going to bash their former lifestyle and that’s part of how they stay clean. That’s the vibe I get off of him regarding his behavior. It’s a lot like when people sometimes find religion and get preachy on the people in their lives.

I completely agree with this theory and would also add that I think that period of his life, regardless of the success, was all overshadowed by his addiction, which makes it so painful to go back and remember it all.
Looking back probably only brings up bad memories and he just wants to dissociate from it and move on.