What's keeping me in the game?
Well, I like the Races. Even though 99% of them aren't clean, it's still fun. It's not that big deal if someone rams me in there, and it indeed isn't a reason for me to quit Races overall. Clean Races would be fun though...
Secondly, open world + GTA + people = nice mix. Even though there is a dreaded system the legends call by the name of "Bad Sport", it is not a reason to quit GTA: Online either.
Thirdly, I don't really have games with the same amount of stuff to do in-game as GTA: Online. Sure, I could play games like Skyrim but that's not similar since it's not Multiplayer. Any GTA singleplayer is good however, but I like Multiplayer games when the game is not story-centered. Single-player is in most cases better in story-centered games.
Fourthly, I'm just killing time until games like Watch Dogs/inFamous: Second Son/Dying Light/basically all the games of 2014 are released. Then I'll be able to get other games to be "disappointed" about.