Like you rightly said, casino business is filled with alot of competitions, someone you refer to a particular casino, the chance is very high that such person might only gamble ones on that casino and then move to another.
So it is pretty much difficult to make any tangible money from referral alone, except you refer millions or user to a particular casino, which is almost impossible for one person to do.
in any business to be successful, the person must create a good business strategy, in this specific case about Referral bonuses, I will have to go back a little to the past, something like 8 years ago... 8 years ago people took us banners provided by the sites (they were banners that had the link with the referral code) so people started posting on various forums and other sites, and even paid for advertising on other sites, but they only had good results when they were going to publicize a new site that they had potential to be popular and the big problem was how to manage to constantly pay advertising and make a profit, this ends up causing long-term damage
so they had to create another more efficient and cheaper strategy, look at these 2 sites:
https://pt.casino.guru
https://www.askgamblers.com/pt
when you look at these 2 sites, you realize that they are sites that have many casinos within the site, so the owners of these 2 sites, when they advertise their site, they have many chances of earning a good amount of money because people enter the site of them and see many casinos, and of course the chances of creating an account in at least 1 casino and making deposits is very high
but these 2 casinos were not limited to just these already known methods of disclosure, look in the menu of the two casinos and you will see that it has written there: "complaints" with that when a person goes to the search engines and researches about a casino, because he wants to know about reviews and scam accusations, that person will find these two sites and in addition to seeing what he wanted, he can choose to create an account in one of the many casinos listed on these 2 sites. even when someone has a problem with a casino, that person will post their case in these two casinos and there is a greater chance that person will also create an account in one of the casinos listed in these two sites. by that I mean that the model implemented on these two sites is profitable, in each business to be successful it is necessary to innovate