You open a new account on a crypto exchanges they will advice you to complete your KYC verifications first, some won't even allow withdraws until you complete the verifications.
Do you think that this was intentional? Maybe to find reasons why they can't process your withdrawal? I think about the same too, but what about online casinos will enough credibility already? I mean very popular online casinos.
I don't think it's intentional in the first place; the reason that your withdrawal is declined is because of violating the terms of the casino ; you will have no issue at all whether you do a KYC or not if you did not break any of their terms, as long as you are confident that you can pass the verification without any issues even if you do the verification later.
Casinos are implementing a KYC later because they want players to test their platforms first; many players have second thoughts about giving their information if they are not sure that this is the casino that they want to play most of their session.