Most bounties state quite clearly that there is no guarantee you'll get paid anything at all. They're a numbers game, or if you know what to look for you, you can minimize the risk of failure.
You should expect that 90% of bounties will fail, so you better ensure that the 10% that succeed sufficiently covers the effort you put into all the bounties you work with.
Even if they fail and their altcoin doesnt worth 1 satoshi, why not still send reward to bounty hunter? I would not mind having this worthless token in my wallet. Who know who would create a buy order on etherdelta or forkdelta for example.
For example lets take Miracle Tele scam projects. There are numerous proofs that it has failed, but trades still goes on according to contract