Firstly I don't like other people enough to want to play games with them and get to know them to join their group and even if I did:
Secondly, I just don't have time for MMOs...
Ha, I actually really like how the "social" aspect of this game works so far. I'm not part of a guild yet, and I'm not really interested in being part of one really. What I do like about it (a refreshing change from the grinding monotony of Diablo III) is that you do see other people going about their business too and you can walk around with them if you want or go your own way. Perhaps you see someone struggling with some enemies that ambushed them so you lend a few arrows in that direction to help out then go off and do whatever you were already doing.
I've definitely been on the other side of that and have been appreciative of someone else passing by and helping out. Even the NPCs sometimes will help fight if you're fighting an enemy near them.
There aren't any obligations to anyone, though, and you can easily solo and have nothing to do with anyone else (I barely chat in the chat windows). But something about knowing that there are other "real" people running around is comforting - playing solo-only large-scale RPGs can be both overwhelming and kinda lonely (didn't get very far into Skyrim or Dragon Age, for instance, and I don't really like to play Diablo III by myself).
So, so far I'm really digging GW2. The MMO part actually kinda reminds me of Demon's Souls since you don't have to directly interact with the other players.