Well, perhaps it makes some big gamblers who have nothing to do with illegal activities feel uncomfortable, but they have to follow the rules of the casino.
As far as I know, high rollers or big gamblers play exclusively on trusted casinos and they don't mind verifying their identity there as this can help in protecting their accounts and money. Those who will feel inconfortable are those who value their privacy regardless of how much they gamble.
Meanwhile, money launderers feel their movements have become increasingly limited with KYC. And there is a possibility that they will ask someone else to do KYC so they can use the verified account freely.
Most of them do this. They pay someone else to pass kyc for them or they use fake/bought documents. But casinos owners are spending a lot of money to improve their security and anti-cheating systems to help them spot abusers.