Bounty managers are only doing their work and they are not the one who make the decision on what to pay to the bounty hunters. All decisions came from project owners but there are few projects who are paying bitcoin or other coins that have a value already.

Bounty campaigns are marketing strategy to all the project owners and they are using it in order to hype or to spread their projects all over the world just to obtain the maximum investments that they can get. So if you are a project owner then there is a big chance that you will use your tokens instead of other tokens in paying the bounty hunters, that's how marketing works.