Games don't need stories.

[Akvod]

Games are funner if there's a stake in them. A bet, pride, real people, etc.

For single player, there's no such thing. Having a story and engrossing people into the game gives them a feeling that they have stake in the objective and goal.

That isn't to say that single player games can't be good without a story, but I'm going to make a risky assumption that every one of you have felt more fun when you guys played a game that was multiplayer (and was of equal quality as a single player game, game mechanics wise), had a good story, had some bet or money at stake, etc.