That was right dude! most bounty now a day want to pay on their own altcoin maybe they have no huge budget to pay bitcoin or ethereum but this is normal on crypto world maybe you will avoid this kind of situation by joining on bitcoin or ethereum bounty payment.
They don't have to pay us with Bitcoin or Ethereum if they think they could make their project run successfully in the future, because I have seen we had that kind of project before that pays you with Bitcoin yet they still failed on market. TL:DR -> Just make the projects run success first, because so far none of them are actually good for now.