The bounty is related to the bounty manager, so they need to make an agreement to hold an escrow or other thing that guarantees payment for the bounty hunter.
This is also not a way out for bounty hunters from working for nothing. There is always a chance that bounty manager, that holds rewards, disappears. As well as holding rewards does not mean they will be distributed. As an example I can point on
KingCasino bounty. Bounty management team were holding rewards and guaranteed distribution. Promoted projects turns to be scam. So bounty managers were holding "nothing" and there was no use to distribute it.