It used to be you couldn't release a game that was multiplayer only and it end up doing anything. Now, with the Internet, we may be seeing this change. If there are enough players online for a game, players are able to then just play online, to play with their friends. Gaming goes back to playing games against other players (or with), and not something that are meant as storytelling devices you play alone.
People are social animals and do want to do stuff with other people normally.