I swear I read something a while back either from Aaron's mouth or from someone close to him that he was having huge issues with the constant touring NIN demanded in 2005-2007 and it took an enormous toll on him mentally. I know he had a breakdown at some point a few years after all of that wrapped up and he's been out of the music scene since.
There's so much behind-the-scenes stuff I wish we were privy to.