So many reasons behind this but the bottom line is that most bounty hunters don't believe in the project of such coin and also they don't believe in the team behind it. I think the best thing to be done by the team behind new projects is to reward bounty hunters with existing coin so as to protect their investors
For most bounty hunters, this is just an additional income. It's no secret that after ICO the price of the token falls almost 10 times. As a rule, most of the projects after ICO disappear, the team stops working on the project. I usually just sell a part of the coins if their price is good.