Well, I'm in my thirties now, and I'm generally not considered a naive person, but I definitely have problems to understand the motivations of people who do this. What's the character trait that triggers this? You don't get money, sex, or booze by cheating at an online game. You might get some WebDiplomacy-coins, but most probably don't go undetected and become a community God so you can sunbath in some kind of anonymous glory.
So, since there's no benefit in your relations with the world outside of you, the whole reward-system must be interior. If I would use a multi, my Über-ich would put my naked Ich in a naked room with a glaring light, accuse me of being the most worthless worm on earth and transform me into Lord Voldemort's helper Wormtail. But apparently, in the minds of those who DO cheat, something different must happen, or at least something else, which is more important - maybe because any self-worth had been destroyed already before.
I just can't imagine what it is - and I cannot believe that such a scary psyche apparently exists in a noticeable part of the population.
How do you explain this phenomenon?