You have to choose the bounty that has a good and reliable manager. If you are feeling depressed that your efforts were wasted that's the other side of bounties.
If they aren't able to reach their soft/hard cap they will never pay your efforts so if you want to get paid with the bounty you are joining. Just choose the bounty that has an experienced bounty manager and assures the participants to get paid.
true, actually i experience too some campaign that cannot paid me. and it is so annoying. so before i join in signature campaign, i will make sure that their token has a exchanger, If not? I will not join or participated.