It is good idea too but many feels its too much to give their KYC details for like they want to try the casino with small amount and in future they will actually play there or not that is why casinos usually ask for KYC when the withdrawal request comes for big amounts, and of course casinos maybe using this as a tool to stop paying the actual winnings from their customer on many cases.
I remember a time I did not have drivers license nor international passport, all I depend on is temporary national identity card, the card is accepted locally but not accepted internationally except when Binance noticed many people in my country have not registered after mandating KYC, but people are using the temporary national identity card and failed, later Binance have no option than to accept it. I was over 18 years but not having the important document for KYC purpose on many sites including gambling site because of the paper temporary national identity card. Assuming I deposit little amount of money on a gambling site, won big, this would be a problem for people tlike me to withdraw.