Addict or bonus hunter I think. I know it's a practice to actually hunt bonuses on multiple gambling sites but you need some friends to do it with you as well as some of them might lose but if 1 wins it's enough. I don't know exactly what this works but here in Romania there are people buying gambling accounts in order to hunt bonuses with them.

The other reasons would be being an addict or simply having a lot of money that you can play whenever you want.