There are quite a lot of reasons why Airdrop/Bounty campaigns do not pay their participants all that much these days, but that which is most predominant is that the project is prolly a scam, thus they only need people to advertise their scam project and the moment they have acquired as much money as possible through investors on their project, they take the money and do not pay participants, because afterall they are scammers.

Having said that, nonetheless there are Airdrop/Bounty campaigns/projects that pay participants, but more often than not the tokens are worthless, you may never even get to trade them on any exchange because the devs stall on the development of the project once the Bounty campaign is over. Overall it is pretty obvious that Bounty campigns are no longer profitable.