List why didn't paid, your experience and history about unpaid projects
Classic reason: market conditions are not conducive.Initially, the irresponsible team delayed the distribution, when they arrived at the promised date they would make another reason and the distribution delay was extended. That continues, one month ... two months ... three months ... then the damn team disappears without a trace, without any news, maybe engulfed by the earth.
There is another reason that sometimes does not enter, suddenly the name and the results of our work disappear from the spreadsheet, without explanation, whereas previously there was.
Escrowing bounty rewards before starting the campaign would be a great way to avoid the payment issue, but not every good project is ready to do that! That's why I haven't seen many escrowed altcoin bounties! Right now only Julerz is arranging escrowed bounties! Bountyhive does the same, that's why people were very excited about bountyhive bounties before!
Yes, escrow is indeed the best way to overcome this problem. This is fair. But that's a risk as a bounty hunter 
just accept it gracefully.