We're a bit spoiled, I guess. A similar question could be "wouldn't you looooove a single-player Counterstrike?" or "...a single-player World of Warcraft"? Yep, we'd do, but there are already games like those. Why should a multiplayer game be single-player as well?
I prefer single player games, but when I'm playing something multiplayer, I prefer it to be awesome at what it does - that is, "multiplayer" (what...a...surprise!). Quake Arena and Quake Live, Unreal Tournament, for example, are just bad as single player games. Heavy Rain would be bad as a multiplayer game.
Some experiences are created to offer a specific kind of "fun". Would a football match be fun if you played alone in your back yard? Would reading a book be fun if you had your friends shouting in your ear? And that's why some games are better as only-multiplayer or only-single-player games.
