There are casinos that ask for documents if they feel that something is wrong with your account and play history. This is applied for special cases and I've seen some gamblers that actually experienced this and told their experiences before because they have found trouble withdrawing their funds.
That's a different matter, the team asked for KYC documents to prove ownership of the account or restore the account to the original user if the report was hacked. In the gambling platform, KYC documents do not have to be required unless if a new gambling platform requires KYC then that is a suspicion.