Not all casinos ask for KYC because many casinos are not too strict on their rules regarding the KYC process. They will still allow their members to withdraw the money without filling anything. But once their withdrawal becomes bigger or the casino sees you do unusual things, they can warn you or directly will not let you do anything with your account. But still, KYC is not mandatory for crypto gamblers because we are concerned with our privacy and do not want to send our documents to other parties easily. The casino know about that and can accept what gamblers want.