Because when it is time for KYC, it will definitely affect the person because no human has two KYC in life. And for that he the gambler has to present the one KYC documents for the two accounts and that will be the place for the casino to catch him.
Actually, KYC is easy to bypass since a user can use his/her relatives, friends and colleagues identities in exchange for money. Some people in 3rd world country willing to do this for payment since they don’t value privacy that much.
The main problem on multiple account was casino can detect IP similarities even if you use VPN to hide your identity. KYC is just a standard procedure of casino when a user violates ToS but they don’t based multiple account accusation solely on the difference on KYC of each account.
There’s a lot of case which a user submit a KYC but still casino decision is still firm because they have IP connection evidence despite the connected account submitted KYC from different person.