It's not hard work to join Airdrops I guess that's why many refer to them as free money, you just need to follow the project social media accounts like facebook and twitter and do some retweeting, this won't take much of your time, can't be compare to bounties that takes weeks and months
This is the main point for involving the maximum number of participants through the airdrop system: obtaining benefits with the minimum of effort. Most often, tokens received through airdrops add to your crypto portfolio numerically and at the same time will have no value - they will remain just garbage. But in general, airdrops as marketing - working well.