I might be wrong, but IIRC the rule to forbid users who resides in restricted country is to be compliant with the gambling regulation of that country, i.e. they forbid users from playing from UK not because they have something against UK, blacklisting UK, or something around that, it's rather because they don't have the permit [and legally compliant] to offer their service there, so they simply can't let people play on their platform from those territories.
Thus, even when someone visiting and not residing, or to put it in a more extreme, even if someone just get past the transit zone [IIRC, transit zone ara considered as a sterile area where you're technically yet to be in the country's soil] and the immigration post, they'll still be considered accessing from prohibited country.
[Disclaimer: I think... even if we access gambling platforms from the transit area of a prohibited territory, that we've not get past the immigration post, we'll still be considered as violating their term. Because eventhough we're yet to be technically on their soil, we still have already entered their jurisdiction].