Airdrops have been long been like that since $UNI airdrop back in 2020, not giving eligibility criteria beforehand was one of major cause of airdrops being worth a lot, otherwise everyone would be farming the criteria and diluting the airdrop.
...And I don't think projects can be blamed here, projects (at least genuine ones) are trying to avoid giving farmers piece of pie, and it's legit hard to filter genuine users amongst those who are good at faking that they are genuine users.
However, some project that i've followed don't even reveal eligibility after TGE and campaign ended which means they like to keep it secret, so there's no deterministic way to calculate how much rewards an individual is deserving of (after TGE).
this kind of project is what I think rather problematic since they are not really transparent.
There is type of breed in projects which take advantage of current airdrop trend and 'farm the farmers' and eventually they don't give any reward whatsoever.
I have been farmed like this in few and eventually you come to figure such projects intuitively, and automatically learn to stay away from them. Experience is best teacher.