The restrictions or banned of gambling in such countries is only adhered that gambling activities shouldn't be practiced or exercised within their territories but the bookies can always adopt to feature them in the gambling activities and it's not illegal if that is being carried outside that country that it's being prohibited.
After all, it was only a sport that is being played and betting sites are only featuring them, so yeah that it's definitely fine and legal on their jurisdiction. Even not sports but a country that has banned gambling, people there or citizens of that country can also do their operations outside of that country. They might only need a permit though, so that they won't be deemed as illegal just like those Chinese gambling operators who are lately on the hot seat. I think that is because they are also operating illegally even if they are already doing this on another country where gambling is legal.
I think it's considered legal because there are no regulations and institutions in the world that regulate gambling globally.
And the government of those countries cannot do anything either, because sports betting providers and online sportsbooks do not operate in their territory.
Also there is no benefit for them in taking legal action for that matter, they can't ask for taxes, etc either because for countries that consider gambling to be illegal then they can't collect taxes from gambling.
It is only an issue if gambling is also restricted on them but a corrupt government can do wonders like they can ask for a bribe money only to let the gambling operators continue their operations.
A lot of gambling operators won't still have an idea about this and they won't bother anymore, so indeed that it is always better for a country or a government to fully legalized gambling because there are plenty of benefits that they can get here. They only need to impose laws of course to lessen the crimes that are happening on it such as money laundering, hackings, scamming, etc... and then in order to prevent the minors from engaging on the said activity.