The simple answer for airdrop and bounty campaing would be :
Airdrop : required us to just register and perhaps to just join their community then done.
Bounty campaign : required us to join and perform some task in a regular way for some period of times for us to get paid.
To be simplify,
Airdrop : Small effort w/ no skills required.
Bounty campaign : Different kind of dedication, strategy, knowledge, skills and talent with a lot of effort in such a long time.
This is the main reason why we are depressed too ( with investors ) when the project is scam or shitcoins is the reward.