I remember the games that get the most people playing and playing actually active are prize games...because there is a reason to play, and to play your best.
The problem with prize games is it influences how you play the game. If you want to win the prize you're going to play to get the most individual glory, which isn't always what's best for the team as a whole.
In addition, certain roles--namely those that perform night actions--are most likely to be voted MVP. If you're a regular townie you have a very slim chance of winning the prize. Since it's normal townies that have the highest chance of neglecting the game the prize isn't going to solve this problem.