The kyc is due to the casinos license. Otherwise Bitsler and every other site out there asking for it would not be asking for it. They have rules they have to follow unless they'd rather shut down.
Exactly, every online casino that is regulated is required to ask KYC if that's the order of the regulators. However, I have an account on Bitsler and I still continue using it without KYC since I did not receive any message for KYC compliance. I gamble on sports mostly, maybe KYC is not for every user?