Except those casinos that are operating in countries whereas it's illegal to run a casino.
I am sure they can do that easily, especially if they make big money from the casino. But each casino owner will have a different reason for making their casino legal or not because there still big casinos out there, but they don't get any license from the government. But if they can register their casino, I think that will work only for the formality in the government's eyes, so they don't try to ask for the "hot money."
It's more professional and they don't have to think of chase whenever the authorities goes visit and check them because they have legal papers to show if they are registered.
Maybe they still want to operate in the underground without paying more money to the government. Or they can register their casino legally, but they still pay some officers to help them. They need to give many documents to verification and validation, including all of their bank account, so the regulations are not checked their business because if one casino wants to register. That will not be good if the owner still wants to cover the other business. But we don't know what they will do so that we could guess only.