Casino platforms typically allow affiliates mainly to grow their business. A person just referred and earn is not possible in casino platforms. As you said everyone will have wagering requirements as well as their minimum deposit amount. There may also be other requirements. A person is eligible for referral bonus only if all those conditions are successfully fulfilled. Affiliates can easily gear up a person's earnings but referring without the terms will only be considered a waste of time.
Of course, the casinos allow the affiliates to grow their business because that means the casinos also benefit from the affiliate program. The casino can get more users joining its casino and if half or more of the new users gamble with big money, and many of them suffer big losses, the profit for the casino will also be bigger. So casino will support the affiliate program in its casino and provide tools for affiliates and offer good commissions to affiliates. Affiliates who earn commissions can usually withdraw the commission money without difficulty; if there are wagering requirements, they are unlikely to be too high. That's why affiliates should look for casinos that have no wagering requirements or anything else so they can withdraw their commission money right away.