"Airdrops" at the beginning were a novel idea to get new coins noticed, but like anything over time it has lost value and been converted into a clickbait type trigger. Ultimately unless an altcoin has an original idea behind it, then all the functionality has likely been covered by an existing coin and it is simply being released to enrich the original "creators". While the original purpose might have been to gain traction and attract miners, it has now become the latest way to pump'n'dump trash. Things like advertising on social media in return for bounties is very much similar to how a pyramid scheme is designed to expand - get existing people to do hard work for pennies while the biggest whales take away huge sums then dump for the next project.