I think for the same reason I do still keep developing it when I could get a job on something else and get way more money... it's real.
What I mean is that we fight, we get pissed at each other, and trust me guys, I've had nights just cursing on some people here and the game itself for failing. Or just to myself for messing up something and thinking how I was so stupid to let that one bug pass through. But at the end, many of us just forgive whatever has happened and continue playing. I've had many emails calling me all kind of stuff and two weeks later apologizing and all being cool about it. It's just like that. (Don't do it often because sometimes I don't let it pass

)
I love it because it's not just an arcade game, we are actually real people, with all the good and bad that comes with it.
So yeah, some have become real friends, some are annoying enemies you can't get rid off. To me personally it's also a personal and professional challenge to do what I do with the game. It's just like real life. There is some kind of charm about it. At least that's my perspective.