I believe most times casinos intentionally do that upon launch to allow traffic to flow in and when they start getting the traffic they desire, they update their terms of service and registered members would not know that until they want to make a withdrawal and the casino requests for kyc and then they would tell them that their country is on the restricted list and would get their account banned or suspended after they had deposited funds to play and won games.
If they do this, they play ugly cards against their customers and this approach only harms their business reputation. KYC if is implemented mandatory or stricter than before, must be announced publicly on their platforms. In addition, the company must give their customers a kind of window time to withdraw fund if they don't want to comply with new and stricter KYC policy on the platforms.
It's better strategies from policies and media announcements from centralized exchanges to online gambling sites. If you don't play ugly cards but have bad approach somehow, your business reputation will be affected more or less, but generally it's not good.