Take a person, put him in a competition where he plays a game next to a person with an audience. The loser will shake the hand of the winner and walk away.
Take the same person, put him on the internet behind his PC and one or more of the following will occur:
He will lose advantage early with an early mistake and just quit the game to start a new one, after all why should he care?
He will be in a position where the loss is inevitable but rather than surrender he will try to be as annoying as humanly possible in the hope that he will have got his revenge for losing or the other person will give up and give him the win.
He will use an exploit or some ultimate game winning strategy over and over again to annihilate 'noobs'.
He'll goad and use swear words and get pleasure out of seeing visible anger in the opponents responses.
He will belittle and revel in success by telling the opponent how stupid or bad he is.
He will play gracefully and say gg when it is over in the face of victory or defeat...
Even if the last one occurs 80% of the time the 20% of games involving the sociapaths and shadenfrauds can be so frustrating for some that it's just not worth it.
Back on topic though, I'm not going to scream against a campaign as it seems a lot of people would like to see it, I just think concentration on improveing large single player games should be a priority. Running a 10 player game with 9 AI is a bit pointless atm. Games quickly turn to boring to watch as the special effects all stop working and the AI turns a bit retarded from sort of mid game onwards.