i don't think they kill the project. the bounties and airdrops help the project a lot. imagine that the project without the bounties, the world won't know about the project. if the token/coins prices dump, i think it's because the projects run by some amateurs team member. the projects will die if the team abandoned their project and do not create the product properly.
I agree with your opinion, dude! Bounty hunters have a job to promote the projects. It makes no sense if they try to dump the projects when the bounty campaign is finished. The reason is that there's no benefit for them to do so! A project will be dumped because of itself, not anyone else! A weak project will dump anyway, do not use bounty hunters as a bullet shield!