It is because the restriction by the provider of the sportsbook IMO, while the casino is using their own terms so the restriction can be different.
That’s correct.
Every game provider and sportsbook has its own terms, which might differ from the casino’s terms. So, if your country is allowed by the casino, that doesn’t necessarily mean it will be allowed by the sportsbook or some of the game providers they partner with.
The difference in the lists of restricted countries are more common with slots providers than sportsbooks, though.
Although a casino claim to be VPN friendly, it does not mean that players are allowed to change their IP to bypass the restrictions by the terms.
I hope Good point! If by VPN-friendly the casino means you can use a VPN to bypass their restrictions then why have those restrictions in the first place?