In my own personal experience, KYC was not compulsary until I made larger and larger deposits and withdrawals from the casino. Especially if you do, deposit then withdraw within a short period of time more often. We can't blame the casino if they check on their users to find out if they're merely using the site as a sort of mixer/tumbler. But if the user is an honest person who merely wants to gamble, then just comply and there's nothing to worry about.
KYC is always compulsory to any casino that has a Curacao license. They just require it in random basis but all the account is subjected to KYC at some point of their game. Casino just imposed it during registration process but you automatically agree to undergo KYC once you are asked the moment you sign up and agree the casino ToS.
It’s not about how huge your withdrawal but depends on the overall activity of your account since you can be subjected immediately to KYC if you show some shady activity.