We are still investing our time and effort with those simple tasks that airdrops requires therefore it is not free because when we are talking about "free" you get it totally free no need to do nothing and no catch. If they use it for their gambling activities then it's their choice and losing it all would be a mistake as they are wasting their time and effort for nothing at all.
Most of us think that is how it works. With little work/effort, with also small rewards.
Joining airdrops just serves as a part-time job for others, so they don't bother to complain about it. But for those who think about earning huge from airdrops will only disappointed in the point that it won't give such expected rewards.
The question arises if it is worthy or not. While more reviewers say it is not worth spending their time and is useless, some also find it good and join. It means that not all see things the same way the same as how airdrops look like.