The incentive for submitting a great idea is sharply diminished by the fact that you don't get to have a say at all in the implementation of it. The project doesn't adhere well to the psychology of altruism.
Yeah, I was thrilled with the $10 million available for funding until I realized that I wouldn't actually get to work on my brilliant idea. Watching someone else realize my dream project would be like some bizarre form of torture.
I'm a busy guy. I have ideas that have nothing to do with what I'm working on. I'd LOVE to just tell someone and let them do the work. Credit would also be nice :)