You had a very nice idea tho I don't think any project wants to do that unless there is strong pressure from everyone, not just bounty hunters alone. Why paying a fee to conduct bounty aka escrow as long as no one can force them to do that?
they have to do that to actually attract more people and investors to invest on their projects, i would rather to join on those projects that store the coins or bounty rewards to trustworthy escrow, rather than blindly picking the projects as much as you can where the majority of them will reward you nothing. i didn't say that no escrow bounty is bad but it's recommended to choose the great one.