I'm also wondering how the system will suspect the underage users. Maybe they will observe the betting patterns. They may contact the user if they find it unusual than all other bettors. And it isn't so hard to determine an underage person by doing some conversation with them.
Probably they still have some restricted countries as they had license before. Some countries have strict laws against gambling. It could be a reason to keep the restrictions on some countries as well.
From all of that, I am only concerned about underage users as underage users can easily access all websites without their parents knowing what they do. For example, the underage visit the casinos and finally, they think that the games are enjoyable. Their curiosity will be bigger than adult people's, so they search for more info about how they can play using real money (in this matter, they will try to have crypto). In the end, they really play using crypto.
The casino will not know who their user that playing many gambling games on their site. However, the casino can observe the betting patterns, that still difficult to determine their users. Even if the casino use KYC to know their users, that is still not easy to detect.
I am sure the casino can apply this for the restricted countries and already had blocklists from the country that can not access the site. Hopefully, parents can take these important jobs for their kids before it is too late to realize their kids have a gambling addiction.