Every casino site has their rules and regulations written about everything like withdrawal limit without Kyc, deposit limit, bet limit, winning limit etc. And it is mandatory for every casino site that if one wants to gamble with big amount then he must complete KYC there. Because all the licensed casino sites always keep a small limit for their customers without kyc because if high limit is given without kyc, the criminal activities like money laundering will increase a lot.
In licensed casinos, all the rules are written in advance in the casino terms of use and other official casino documents, and when starting to play at the casino, all players know these rules in advance to follow them.
And that is the problem, when a gambler opens an account at a casino they never read the terms of service, they just want to gamble immediately and they are in a hurry to try the games offered there, and then when they are requested to go through KYC they complain about it and they claim that it is unfair for them to go through that process, but since they accepted those terms then they have no other option but to submit their documents if they do not want to lose the money they currently have at the casino.