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 needs KYC documents to prove ownership of the account or return the account to the original user if the report is hacked. In the gambling platform, KYC documents must not be requested unless the new gambling platform requires KYC then that is suspicion.
Yes, as I said it's for special cases. I have seen them post those problems here and disappointed that they were asked for it.
This will make others aware that if their account is being taken as a special case then they have to obey so that they'll be responded very well and clear and, they won't be mislead/misquoted.