i don't think it has anything with believing in the future of their token because the creators of these tokens know better than you and i that their token is useless and worthless.
the only reason why they pay in their own token is because it doesn't cost them anything! if they wanted to pay in bitcoin for example they would have to spend money and buy bitcoin and then pay people. but when they pay in their own token, all they have to do is just create them out of thin air with no effort or cost!
They don't have to buy Bitcoin or eth or any tradeable coins because they can get it in their sales and if they didn't reach their soft cap they will not pay their bounty hunters, all ICO is like that they will not pay bounty hunters if they did not reach the soft cap
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.
He can suggest this and besides some bounty managers are members of the team, majority of bounty hunters prefer tradeable coins and they will prioritize this project.