Apart from scam bounties, the main problem affecting bounties is overcrowded bounty hunters, even if a bounty has good allocation either trading already or not if bounty hunters are way too much it won't matter and even the work won't fit the payment, who is with me? Escrow isn't even the most important here, some may say otherwise but to me limited participants will get the job done
Developer need more exposure for their project to increase their success rate that is why they are not limiting the number of participants for their bounty programs, maybe you try to implement this when you become a signature campaign manager here.