Almost all casinos have restricted regions that are not welcome and that is not because the casino does not like people from that region but to prevent jurisdiction that could extend to sanction the casino for not having a registration in their region before allowing gamblers from their to use the casino.
Casinos doesn't want to get a trouble from allowing those people from country that ban gambling. It is a prevention from the casino but we know that those people can still visit the casino easily. Casinos can not prevent from those people so they just see the reality after those people verify themselves.
Talking about countries that ban gambling, in my country gambling is made legal yet people still get restricted from joining most of the gambling site here, does it mean that this casinos/gambling platform are built in such a way that other countries will not have access to thier gambling/ casinos site except you're a citizen of such country? because I feel that this could be the reason why they will choose to restrict other countries from accessing thier gambling platform.