Casinos don't really make this rules by themselves but rather some regulatory bodies and also the gambling board  a d this casinos only follow instructions given to them by this Bodies.
There is this prove of income verification going on with stake.com and I think this also another way to help comb this criminal activities and ensure customers safety.
We are in a society were everyone wants extreme privacy and most times, people shy away from casinos that seek or require KYC before registration or after deposit and this tends to want to keep their customers, hence making them break some rules or taking some drastic actions.
I suggest that a strict KYC should be implemented in casinos without compromise because this will go a very long way to reduce money laundering in casinos.