But the regions are connected to the earth because of those silly things called "tectonic plates", instead of floating in the ocean. If that wasn't true, maybe I could go get authentic Chinese food right now. Besides, I will take this quote from the original Black/White versions:
"Professor, my plane is a cargo plane! It carries cargo, not people! And you're talking as if places like Kanto and Sinnoh are right around the corner!"
This suggests that all the regions are indefinitely far away. Why would Hoenn crash into Unova, and not Johto or Orre?