That is how gambling sites are. Most of them will not demand for KYC from you as long as you are losing, but if you win and want to withdraw some money, they will go through your account and tell you to do necessary things before you can withdraw and requesting for your identity through KYC can be among the requirements.
My topics originates from the comment of this user above in this thread where the OP is writing to seek about KYC stuff. The link to it will be at the end of the topic.
I know casinos do this. I have experienced it too. It is also in their T&C. My question for casino lovers is that instead of waiting until we win big and are asked to submit KYC documents, will you do it before the casino management or administrator request of it? Is there anyone who has gone ahead to fill out and submit their KYC on their account or by asking their customer support for it way before they even start make a request.
Link to original post described in the OP - https://bitcointalksearch.org/topic/bcgame-asking-for-kyc-before-letting-me-withdraw-5494948