If they use big money to gamble and it turns out they are using gambling as a place to launder money, they object to KYC and will take issue with it.
Especially if there are new members who have just joined and immediately used big money to gamble, the casino suspects them and asks them to do KYC.
So casinos don't want to take the risk if there is illegal activity at their place so they can just ask the new member for KYC directly.
If you are new to the casino, it is better not to use big money right away and try to be patient to continue using small money to gamble.
I think the casino will also see your journey in playing gambling at the casino so they won't ask you to do KYC.
Not everyone will do something like that. Those who disagree with KYC are of course also due to privacy issues, because KYC must provide real identity to be able to make a withdrawal process in a certain amount.
Currently, the regulations in each online casino tend to apply KYC for security from money laundering practices. New people who make large deposits do need to be aware, this will also have an impact on the sustainability of the online casino. Casinos that apply strict rules will mark these transactions.
I am also relatively new to gambling, making several small deposits is more recommended because there will be no suspicion related to money laundering.
Performing KYC is mandatory when withdrawing a certain amount or just asking for complete identity without supporting documents.