It's not them but the government that requires the implementation of KYC. If there was no mandate by the government requiring it, they wouldn't mind accepting gamblers on their platform even without KYC, as that would be easier for them and they could easily attract gamblers. However, as the AMLC is strict in doing its job, they want to prevent or minimize money laundering by criminals, and KYC is just a basic implementation they need in order to trace the transaction's owner and its origin, of course.
Yes, it's from the government but casino see a chance for them to know their members by asking KYC to their members so casino can check all of their members. Casino will only follow the regulation from the government and wants to safe their business and apply KYC for their members. With KYC, casino can check their members and if they found any suspicious thing, they can investigate immediately and report it to the government.
Casino can block their member temporary while the investigation and make everything is clear before they allow their members can back to playing gambling in their place. Casino wants to prevent the money laundering in their place and using KYC, they can know where the money flow so casino can do something if their members do an illegal thing in their place.