Humans can have a tendency to invest heavily in their online or fantasy lives/personas when their actual lives/personas in reality are lacking in quality, content, and/or activity. That would be my first guess as to his motivations, anyway.
That being said, there's not too much shame in it. Many people spend the majority of their free time escaping from reality, whether it's in an online persona, a video game, a television series, a movie, etc. Or some people just escape into their own minds, dreaming up all sorts of things that they more than likely won't see in this reality, at least not in their lifetimes.
But lastly, that's just one suggestion. People can be complicated, there are other potential reasons for the sort of behavior that he exhibits. Delusional self-righteousness, extreme paranoia, the thrill of manipulation, all sorts of reasons! But usually even those reasons have reasons, but you have to start somewhere.
Thats his job on the forums. Supreme Butthurt has his job of being summoned, Lost Sols has his job as our collective voice with all Destiny related problems and Solaris just archives stuff... I guess. It's just what he does.
Everything posted on the internet is forever. If you're concerned.. choose what you say wisely.
And threads about individual users are equally creepy. Just throwing that out there Mr Alt.