Quite a lot of Bounty projects that do not pay bounty participants even I can't count anymore, Some of the reasons that I got were that the Team postponed delaying payments so the days passed they deceived all bounty participants. The support that I expect for all bounty managers must use Escrow to manage bounties.
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! That's why I haven't seen many escrowed altcoin bounties! Right now only Julerz is arranging escrowed bounties! Bountyhive does the same, that's why people were very excited about bountyhive bounties before!
yeah, it is not that there is not many projects that want to escrow rewards, it is mostly that project do not want to do that, and this is way most of them could scam the participants, but since there is many people ready to support projects that do not want to provide escrow, they will not cease to exist, or to be precise they will be most of the projects on the forum