I also think of the same thing why does some hunters rush on joining bounty when their previous bounty ended they should choose carefully or wait for a deserving bounty to promote.
I feel like some of them doesn't really care and just want to join any bounty that they could and try their luck on it.
Of course I agree with being patient and not to rush into any new bounty campaign as soon as the last one ends. But sometimes you can never avoid getting scammed if the project doesn't want to pay the hunters from the very start.