I think Ethereum has been around for a long time before covid tragedy. When I got to know BTT around 2017, there are already many projects that used ETH tokens to pay bounties. Likewise with Airdrop, it has also been around for a long time. As far as I know, airdrops only provide small payments and sometimes don't even have any value at all, maybe it's in accordance with the task that must be completed.
About big payouts on Airdrop, I think it's impossible. Of course, project owners will pay people who can improve their trends or make their projects successful. While the airdrop is a free gift for testnet or celebration of success, there is also a lot of participation. So it's impossible to get good pay from airdrops.
So far, I think Signature Bounty is the best. But unfortunately currently many projects do not include signatures in their bounties. I hope that later there will be more potential signature bounties present to enliven the BTT forum.