Escrowing bounty rewards before starting the campaign would be a great way to avoid the payment issue, but not every good project is ready to do that!
You are right. Every bounty manager should be better if escrowing the rewards before starting the bounty program. It is an effective way to prevent unpaid reward issues. We can see that most of all bounty managers who provide their campaign on
services board have escrowed the rewards before starting their campaigns. And we have no problems with the payment distribution there.