This is the truth these days. Before, we saw those casinos that were okay with no compliance prior to KYC. But today is different, everyone will be subject to it especially if you've got huge withdrawals and they'll have to ask you those certain information that they need to verify you as the genuine owner of that account and as well as them complying to their rules of operation. We'll never see today a casino that don't have the rules about questioning a user for kyc suddenly or the rights to ask the user a kyc.
But its understandable right? As you said mostly when there is sudden changes in the activity of an account will trigger the security system of a casino which may put the account on hold until the further process comes officially, yes its bit annoying but also it can save someone's money if the account accessed without authorisation from the actual user.
If I recall I experience this on an exchange after I changed my password the withdrawals are then paused for some hours it only sucks though because I urgently needed the fund that day but what can I do? It didn't come to my mind that I will contact their support to make an exemption to my account and to fasten the waiting time.
If this occurs to a gambling site I think I will feel the same, ill be disappointed and bored if this happens after I deposit my funds because I can't play gambling since my funds are frozen. Maybe they can make this feature optional and not mandatory since many of us know what we are dealing with. Our accounts will be just fine.