That's why I already stopped joining new Airdrops.But in some cases you can make money by joining legit airdrops.And If you can refer some users then you can generate a decent amount from Airdrops.
referal will help us to boost airdrop reward,but its not happen to alll projects. so far i know airdrop program have limitation participants or all participants will accepted. both of this scheme will influence airdrop value , more people joined we will get less reward just like bounty campaign.