Firstly, i want you to understand that it not every project that didn't pay their bounty participant end up scamming their investors. However, there's no way we can stop scammers cause they will always figure out another strategy and the best thing bounty hunters ought to do is doing research about the project (which what i always do) before participant in their bounty.
That's right, not all projects not pay Bounty participants, most of them pay, but the next problem arises where their tokens are not valuable on Exchange, of course this is their trick creating shitcoin to be sold to investors. Scammers only look at investor bags, their target is to take investor money.