Airdrops were so popular among the crypto-community over the years. One of the key features of the airdrops is, it gives every participant a chance to get some free tokens by completing few tasks. Most importantly it is totally free of charge. But nowadays we frequently see a trend where the organizers of some of the airdrops ask to send a small fee prior to sending the tokens. In some cases, they put a condition saying that in order to withdraw tokens or any fund received from the sale of tokens, it is mandatory to take part in their ICOs. I would rather call such events as "Scam-drops" as they not only dilute the meaning of airdrops, but also make people to move away from future events due to lack of trust.
Up till now, airdrop are still popular and I believe 90% of the people who still partake in airdrops are noobs in the crypto space,most of them decided to try it out after hearing about airdrops that made people rich, e.g uniswap airdrop, I think over time they will discover that airdrops are not profitable at all, and about airdrops that requires sending of gas fee to receive the free token or a must to participate in their ICO, I will advice everyone to stay away from such airdrops, it's definitely a red flag for me, cause you performed some tasks to recieve that free token, why should you pay to get it?, that means it's not free 
, those airdrops are normally organized by scammers trying to steal from the poor airdrop hunters.