ICOs have been very popular. However, ICO is heavily developer favored program.
Let's say they produced 10000 coins and each worth $100, and sold 9500 coins to the public durin ICO and kept 500 coins for dev themselves.
The dev raises $900,000 initially, and left with $50,000 worth of coins for themselves.
Ideally, the dev continues the development of their coin or services to increase the value of their coins.
However, to raise more money, it is way much easier for them to run away, and start another ICO project, than continuing their development works.
This is the reason why ICOs are heavily developer favored, and very risky for the investors.
Now, let's talk about airdrops. Airdrops are investors favored, since they don't cost the investor anything for the most part.
Because the developers do not gain any money in the beginning, they are required to put effort on development, in order to increase the value of coin to earn money.