So this might have already been covered in another thread. If so please direct me there but there are so many threads about this subject I am not sure if it has been covered. So even with the idea that humans can only travel via escort through the portals I had an idea I wanted to ask if it has been covered.

Once they are on the island or habitat whats stopping them from just staying there. It is supposed to be a self sustaining community. Maybe they have humans that live full time on the island and just never leave it. Like some of the X-Men allies from the past that might be persecuted for being mutant lovers.