Maybe it was just you with that thinking. There are both good and bad bounty projects. Of course, after the bounty promotion end, a bad project would lose its hype and got dump not matter if the dev want or not. Don't fall for the hype and research to make sure you join in a good bounty project.
This reminds me of the Electroneum bounty, when the bounty is distributed it has no effect at all on the price, instead the price of ETN actually rises
maybe some projects do dump but it depends on the developer of the project
Of course it depends completely on the project itself, in fact a sign that the project could be a good one is to keep in mind when the distribution of tokens is going to take place to bounty hunters and see if the price collapses when bounty hunters begin to sell their coins, in most cases the price will go down significantly signaling a bad project but if the price does not go down this means there are many people buying the coins, that the market has enough volume to absorb all of those coins and that there is a lot of interest still remaining in the coin itself which most likely signals a good project.