amcdermo: There does seem to be a lot of multiplayer only games released recently. I see a new fps on Steam check out the game page and nope no single player. It's as if an individual or small company have decided to make a game and the quickest and cheapest one is an mmo using the Source or Unreal engine.
Well, the engine isn't the important bit. The thing is, a good singleplayer experience takes a lot of time and effort to design, because everything that happens to the player has to be provided by the developer. AI programming is difficult and time consuming. With a multiplayer game however, no AI programming needs to be done, no event triggers need to be made, just the basic game mechanics and the levels. Then the players themselves provide everything else. Note that I'm talking primarily about PvP multiplayer games. MMORPGs usually need to incorporate non-player enemies and loads of event triggers as well, so not much is saved with those.