I think there is many types of airdrop. Usually its some sort of promotion. For not so long ago there was a big airdrop of stellar. Alot of money to alot of people, for only signing up. The most airdrop you see, are not so straight forward. Either they are scam, the buisness shuts off, or you have to do many complicated task before getting some coins. But sometimes, when you keep a eye open, there is good airdrop, which are easy, and can be lucky to get some cash. But it's not a giveaway, altought it seems so, airdrops are usually promotion.
But how would they profit from giving away cash so easy? I dont acctually know into details how it works out. It may be very different