Have you ever gone to a supermarket where there's a hotdog stall that offers free taste. That's also the same with these airdrops, they are attracting people all in all by giving such tokens for free.
That makes these airdrop people announce and tell others that they've found a good token which results them to advertise that project.
Yes I do understand the tasting part and was thinking exactly the same until I started reading BitcoinTalk where non of investors mentioned Airdrops being at least one of their Altcoin discovery channels.
I know that for some ranking sites, there should be established community to get a good ranking, which mostly is acquired via Airdrops. But then it is the same as buying fake accounts to have just a number to get better ranking. I want to see if I am missing something?