Yes, I do agree that those personal details provided to these airdrops may be fake and users may not even check their emails they receive in those accounts so if someone buying those details for marketing their product may not be worth.
Its not fake per se. Those are users but the number of false results from it are much more. There may be genuine users who are new to crypto and want to get their hands on some new coin and so they had joined the airdrop. Many of the newbies here have been airdrop hunters for sometime hunting shittokens and we also have airdrop listing sites where they get listed.
Some of the ICOs turned to airdrops good example are STKtoken and Viuly when they were having problems reaching softcaps. Still most of thee database is alts and thus they need some method of weeding out these shitposters before starting a social campaign.