Take note, Casinos will ask or demand a KYC if there's a big winning involved, is this one of their ways to scam their players?
It is a debatable question, no matter how hard to accept this fact it is still one way for casinos to verify user identity. I personally don't deposit as much as the amount that can be subject for KYC verification and it is not safe to share personal documents with third-parties. The same idea is true for some crypto exchanges as well. 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.
Some casinos will ask you for KYC even if you haven't deposited a lot of money because they might suspect that you are not who you might pretend to be, they sometimes do it after seeing one's betting pattern or maybe if someone is winning a lot especially in sports betting. Some casinos even ask you to complete your KYC right after you make a deposit only to make sure you don't do something.
What I believe in is that if a person doesn't trust a platform with their personal details and documents, they should simply not gamble with them and find a platform that they think is trustable and they won't have any issues even if they are asked to complete KYC verification at any given moment.