I'm still wondering why developers will organize airdrops and distribute an amount of tokens which is far lesser than the minimum amount of the tokens that can be deposited on an exchange for trading. If you don't want the users to cash out the money, why do you let them waste their time?
I think that it's made as a part of marketing strategy. But I don't consider airdrops as an effective advertisement. It may have some effect but bounties are more worthy all way.