Specially when making large withdrawals, after big wins, kyc is expected.
There are many reasons for such. Regulations, taxes purposes, etc...
It's also a compliance on the casino for allowing that to happen. If we customers are being pressured by the casinos to comply for their KYC approach. They're also as well as a business need to obey the regulations that they're being enforced with. It's a legal business and so, they can skipped that.
There are very few casinos which doesnt perform kyc, but they are usually much smaller and simpler.
For small gamblers, they don't mind asking them KYC but eventually they'll also get to them.