I myself, am not a part of any of these such communities, but I have friend who are. The friends who are, are a part of World Of Warcraft and groups like that. These friends, to most, would be considered nerds. Most would be considered socially awkward and loners. I think their motives are the same as what motivates most people to do, well just about anything: Connections to other humans. WOW provides something they enjoy (intrinsic motivation) and a connection to others who enjoy the same things.