Most sell because they do not have any other source of income. As you can see bounty hunters are from predominantly Asian or Developing countries. There are few Europeans like us oldies doing it for a living.
Also, they don't care about the tokens, they just want bitcoin or cash as their immediate end game.
Only a few bounty hunters are real crypto-enthusiasts who would hold some or a portion of their tokens because they actually believe in the projects they promote.