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.
As much as this is true, i would say that, there are still some gambling casinos that are truly honest with their referral system and bonuses, it is just that most gamblers don't or fail to read and understand the casinos terms and conditions regarding the referral system.
Some gamblers do think that casinos pay them the referral bonus according to the number of signups that join the casino through their referral link, but in reality, it is absolutely not so, most gambling casinos i know of will only pay a gambler the referral bonus when the person or user he or she referred deposits money, and gambles on the casino, the casino will pay the user according to the amount of money the referral deposits on the casino and possibly wager.
But unfortunately, this is something most gamblers seem not to understand about referral bonuses.