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!