North Korea allows limited number of foreigners on their territory either as residents or tourists every year. Krakoa allows no one, period. That simple and that's their official policy stated by their ambassador to the UN.
Again, they are not the only country to hold such a stance. But that's not the stance of someone trying to coexist is my point. No need to make it pass for that. They have other priorities like establishing themselves as something other than a fledging territory, so it's relatively understandable.