I have already made a Deposit to this casino several times and even made a withdrawal 2 times, and the KYC procedure was not necessary.

Yes, KYC or any other document does not require you because the deposit and the withdrawals you made may be small. But when it comes to big issues, they will start restricting, asking for Identification for KYC purposes, and requiring documents. So, it depends on the player how much he will enter and release money.
This is not fair because if anyone wins a big amount it is the responsibility of the casino to pay him. They should not delay the withdrawals by asking them their kyc 's and rejecting them and denying withdrawals. These are the tactics taken by the casino's to not to pay to the gamblers.