Projects are conducting airdrops to make their coins and projects idea spread out. I think it is one of the teams strategy to reach their goal. We can't exactly tell if the project that has airdrops are scam because every ICO project do it depending on the teams desire and plans. I am actually one of those who are hunting for bounties and airdrops and based on my observation airdrops helps the project be known to some was not aware of it. If it is not a scam it can be profitable to both hunters and the team.