I believe that Binance is a cool exchange that allows its users to earn money without even investing a bunch of airdrops, a bunch of referral contests and much more in general, I would even recommend it to my friends
Binance was not a cool exchange because the earning free coins they cause Binance was actually a cool exchange because it usually be the first exchange to create or integrate new innovations in the crypto exchange setting.
With that been said, there airdrop participants indirectly make an investment (since they have to some certain amount of BNB) before they can earn free coins and this is Binance own way of encouraging investors to buy and hold BNB.