Including every region in 1 game takes away the purpose of buying the other games. Plus, the way the games are currently programmed, you'd be near level 100 by the end of region #2. With 4 more regions, they'd have to totally redo the leveling system.
Plus, these stories are all stand-alone and should be left like that. I think it's just much better to leave the games as they are.
for "every region in 1" to be feasible, the change they'd have to make on the systems, movesets, etc, would have to be so big (to keep it playable AND enjoyable) that the idea is automatically dismissed.
the development would simply consume too much of their time and money.
besides, how much would you be prepared to pay for something that big knowing it will eventually become outdated?
another option is to make an mmo, but i think it's pretty clear they don't want to go that route cause:
1- they WILL keep doing main games for handhelds only
2- they WILL keep the story on single player
yeah, i know it may look good on paper but as soon as you stop to think about it realistically, you understand it won't happen.
unless, for some reason, they get desperate in the future and do it as a last resort.
there's a huge difference between cool and reasonable