Any time a casino asks for KYC, there should be a reason for it.

If they determined that the user was multi-accounting without the information from the KYC, there was no point in requesting it and thus they are merely using the balance as a hostage for the gambler to relinquish their dox. If, however, they determined that the user was multi-accounting with the information from the KYC, then they should explicitly state this.

But if you ask for KYC and then say, "you're multi-accounting," without any indication of why... then you're just getting KYC from desperate gamblers for free, and that is completely dishonest.