The fact is that their work gets accepted because they followed coding standards and understand how to not undermine the project design. But people who have not internalized coding standards or the overall project design will not see that and get upset that they don't get paid for at least showing how to solve the problem. (Nevermind that the part of their solutions that they point to would have been obvious to anyone.)
So that he does not have to pay bounty.
As a side note this particular perverse incentive also exists in the world of proprietary code security bug bounties. That's why bounties cannot grow to truly enormous amounts.