The casino does not want any of its members to be involved in illegal activities, so they will always monitor activities and ask their members to do KYC when they want to withdraw their big winnings.
I seen some new casinos who do not want their player to win big and withdraw that amount easily, They ask for various documents for KYC, many different kind of documents like bank statement with transaction id for all transactions, paycheck, electricity bill, passport, etc. I once made an account on a new casino by seeing their bonuses, I deposited first time it was deposited with no problem, Then after busting that amount I deposited 2nd time but that deposit was not arrived I contacted support for it, that my deposit was not arrived in my account, they provided the casinos finance division's email for sending the issue, They I got a reply from them after 2 days they asked for various kind of documents, that was around 12days long process because they were so slow to reply on emails. after all until today I didn't have got my refund. so stay away with new casinos which offer huge bonuses or bonuses which seems suspicious.
It all depends on the kind of casino company you're dealing with. Some of the new casino companies does request for the KYC in their bids to deny their customers payment after winning huge amount of money while long existing and popular casino companies do ask for KYC so they can verify the customer wether he's the true account owner or an an imposter. For the long existing casino companies, I think it shouldn't be a big deal to provide them with all requested documents that'll prove you to be legally fit enough to claim your winnings