Are these mutually exclusive? Why would you have to forego that salary to work on this problem? This is one of the most prestigious and meaningful problems in all of mathematics, which is why it has such a high prize amount attached to it - why would a university not support a mathematician working on such a prestigious and important problem in lieu of something else?

Publish or perish? We're talking devotion here -- so no time to do anything (like edit proofs) other than try to solve the problem.

[Edit: my only point here is that the prize is probably not driving human effort to the limit.]