Referral bonuses are just baits to win people over. In reality, its not what its actually presented as. The conditions are always vague until it gets to withdrawal, thats when you actually know whats at stake.
So they get gamblers in through those ref bonuses and promise them juicy offers and at the end of the day, you have to either commit funds or you are required to hit an almost impossible target to receive the ref bonuses in reality.
Exactly, I saw some of them just now, guy I became tired of the promotional bonus in the sites. I was just asking myself if those bonuses can be withdrawn. 1 BTC to 5 BTC as bonuses. Really as you said, they just traps and nothing more. And now because the referral bonuses are big so for those gamblers that do not want to play in the casino would be attracted to sign up to them and thinking the bonuses will be withdrawn but it is for wagering only and even they think that they would used it to win so they can withdraw the winning and another big irony again. So everything became frustrated to them. Referral bonus is part of the advertisement so we should not blame the casinos but they should use a moderate amount for the bonus and make it reality because those big amount some are using when you registered, you will not even see the bonus. And some scam sites use this referral bonus to lure gamblers to sign up and be scammed.