Because the legitimacy of crypto gambling site is depend on how the gamblers trust them for long years.
If the casino is legitimate in business and have the good responsive support team to handle the issues the players will stick with them for years wagering on their favourite slots and games.It also depends on what are the marketing techniques for casino that binds the players and keep them interested in playing over their site.
I think it's more about promotions as well, it is a competitive market and having some working great promotions will keep you playing. Lets assume that you have staff that helps the gamblers out whenever they need it, and you also have promotions to make them gamble more and stay here and keep gambling, that means they are not going to leave, because there is no reason to leave to begin with.
However, when you are talking about the places that do not have big promotions, then people could like the place, but if another place offers great promotions then they will have the urge to go check that place out and maybe gamble there because it would be a lot better. I personally hope that it doesn't happen that way and it goes to show that promotions matter.