airdrops are indeed (most of the time) a waste of time. But you have to think about it kinda more logically, you are expecting to make money by just submitting your address.. I mean what do you expect? There is nothing free in this world and there is definitely no one willing to give out free money to anyone else. The only reason projets are doing these things are for advertisement purposes, they want to make sure that the product and service is heard, and what's the best thing to do that other than sending you some of that product/service (coin in our case) to use it yourself. It's basically useless and airdrops have had hardly any financial effect to anyone (expect some serious projects that managed to do something big) but you an count this on your single hand.