The airdrops are giving free coins or tokens for one time small tasks. The project's owners need to boost their social media profiles for small rewards. That's not bad. A year ago airdrops have given decent profitable rewards. But now airdrops are famous and getting a large number of participants. Then each participant not getting profitable rewards. Another thing is scammers using this airdrop method to boost their scam social media profiles for nothing. Then we hard to get profitable rewards from airdrops.
I've heard the good time about Airdrops. I have this doubt in my mind because I actually lookup on twitter of an airdrop I just did, a lot of the tweets were made by new accounts(no followers/followed account, even no profile picture; all their feeds are airdrop required template tweets). To me it's just sketchy, like ppl now dont bother to get to know the project before they do airdrops. And on another side, the projects are giving less and less because the social media boost from fake/new account isn't working out for them(This is only my assumption though).