To justify being an mmo and not a single player game though doesn't the story an mmo have to tell arise because of the players?

The stories that arise in mmo's now actual kind of reveal the true focus of the game: loot drama, guilds breaking up, ninja looters, etc...

I think if the games focused more on the world, and had a mutable world that players could really feel apart of that the dynamic of the game could shift. Playing a single player game that has a great story, just on a server with other people can be fun but at what point does it make more sense for it to just be a single player game?