Most of these casino just do all these because of the government rules that are tied to them operating their business. These casino are now implementing all these to avoid be sanctioned of money laundering law because most of the users deem their site to be a perfect spot for huge deposit and withdrawal which can cause lots of attention so that's why KYC is been called upon
In the past, the casinos were blamed by the government for harboring money laundering. A lot of them were either closed by the government or went offline, which caused issues for the users who had their deposits in these casinos. That is the reason why KYC is now being made mandatory in almost all online casinos. A few exceptions are there but sooner or later they will also implement KYC. With KYC you no longer are anonymous but as a user, you still have the anonymity factor with other users.