Bounties, in general, are more risky than campaigns paid in bitcoin, and usually manage by renowned managers.
Bounties run by companies that do their crowdsale, fund-rasing, IEOs, ICOs, whatsoever, and they use their free coins, free tokens to do that.
At the ends of those ICOs, IEOs, if teams fail with their original purposes, don't collect enough funds they wanted, they might shut down their projects, make scam exits, for instance; then participants of their bounties will end with zero, zero payments after weeks/ months of hard-working.
Personally, if I don't find campaigns to join, I am free, and I will maintain to stay away from bounties as much as possible.