It is also understandable, the casinos would be broke in no time, because everyone creates hundreds of accounts to grab the 100$ several times.

I have experienced very few airdrops in my playing career that have actually allowed an instant-withdraw. Most of the time efialtis advertises these via his site btcgosu.com or even organizes extra promotions that are only advertised via btcgosu.com. Something like this then already pays off, but is unfortunately very very rare.