Airdrops can make you a millionaire only if the coin is a good coin and not a shit coin. 

I know of someone who made a million from just one airdrop. He filled it and after some months, the coin hit over $100 and he sold off the coins he got for free and it was worth over a million.

Although, there are so many shitcoins that you don't even know which is real or fake. It may take a lot of your time but with your determination, all your airdrop coins may eventually make you a millionaire.