Why services which want to launch on EOS main net do airdrop?

[sadless]

I want to know the exact reasons why the services listed below link do airdrops.

https://www.eosdrops.io/

Why they do airdrop instead of ICO? Are there any specific benefits when they do airdrops?  
Most of them airdrop their tokens to others without any conditions instead of using airdrop as a marketing method (The one who joins a telegram group can get tokens for free.)

[IgorShumilo]

The advantage here is only one thing, this is that you will not spend your money for investment in this project. And if the project turns out to be a fraud then you will not lose your money. I like this version of ICO!