Airdrop is a free tokens or coins to the crypto community by doing some tasks.
Some airdrops requires you to like or follow their group account and repost / retweet some of their announcements or you need to join their telegram account. This form of task is method to gain more popularity.
It was an easy task to have free coin. So you should continue participating airdrops because you don't loss anything, just exert small effort to do that.