Intrinsic vs. Extrinsic rewards was a recent Extra Credits presentation.
They boil down to a question: "Am I doing what I'm doing because I enjoy it or because it can get me something I enjoy?"
This is a good question to ask your players -- what parts of the game do they personally enjoy the most?
Are there any parts they do because they enjoy the result, but not the task?
As a LARP player, I find there are scenes I need to be in because of extrinsic reasons: I want to earn status or prevent something I care about from being harmed. And there are scenes I want to be in because of an intrinsic reason: I enjoy novel puzzle scenes, spotlight time, intrigues, and acting out ritual behaviors (such as coronations or knightings, or vampire court or magic rituals).
As a tabletop player, I find that I intrinsically enjoy scenes that let me have influence over the direction of the story or fate of NPCs; or game scenes like puzzles and tactical combat. From that, you can probably see why I wrote a post that urges GMs to focus on the boundaries (story) and scaffolding (game) limits for sim scenes, instead of focusing on realism, verisimilitude, and pathos. I need a little of those things to enjoy the game, but not much.