If there would be a legit and sure way to get big airdrops, everyone would be using it and after a while that technique would be rendered ineffective as value is based on scarcity and you can't just gift everyone something and expect it to have value.
This is precisely what has happened. In start, retrospective airdrops were rewarding substantial amounts, as this trend got saturated and people started farming for potential ones, qualification requirements gone high while reward got severely less.
This is also the reason I don't expect much from layerzero, zksync but I'm curious how they gonna turn out.