>>28109181Unlike our world, pokemon regions are highly isolated from each other, with the exception of some (Johto and Kanto).
The idea of travelling to other regions and connecting with them is very recent, that's why we only see a few Gym Leaders and travelers moving between places.
Speaking of Gym Leaders, the whole pokemon league thing is a really recent trend, one that Alola hasn't have caught up with yet. That's why the gyms look more modern compared to the cities they're in, because they are usually 1 or 2 years old, and that's why the champion is so underleveled in some of them, because the institution isn't as new in the region as in other places.
Our perspective of "New" regions and pokemons comes from the Pokemon Professors association (?). They are discovering the new regions and pokes at the same pace that we are, that's why the dex keeps expanding. Each generation's Professor has only recently been relocated to the new region, which explains why their research is usually new and why they need 10 year old volunteers to recollect info of the region.
That's at least how I justify the Pokemon World accidentally "discovering" 200 new species, and why we don't know of new regions until Ninty announces them.
