Maybe they use this method to scam big winners since it is rare to see complaints about the casinos which block user accounts that lost big.
It's possible, but I doubt most casinos will rely on that method when they can handle these KYC cases much better.
So any amount below this amount can be withdrawn without KYC verification., so at that it becomes mandatory to take note of the balance and amount you want to withdraw in such an account.
Some casinos might have these rules, but if you're lucky, you can even get away with it. In one of the gambling sites i've played, I was already above their threshold, but they're still not requiring me to go through KYC.