I don't think that this statement is really accurate. I am leaning more towards believing that most bounties are a scam and only some are legit. A scam bounty is not just a campaign that doesn't pay you for your work. Even if you get paid with worthless tokens, or tokens who were already dumped on exchanges by their creators before they were distributed to investors and bounty hunters, that is still a scam bounty. Or if you get tokens who will never be listed anywhere.