Here, have a look at this...
"NO. Let me try to put this in a way you can understand...
You know how Ash never uses any of his old Pokes in the anime? What fun would it be to battle Gym Leaders when they have a Level 13 Nosepass and you have a Level 65 Blastoise? There's no fun in that, it would just make traversing the region a chore. You'd probably say, "Oh, just level up the Leaders like Gold and Silver did." That's another problem.
Let's say you start in Kanto and beat the E4 + Champion, then move on to Johto. Your team upon entering Johto would roughly be around the 50-60's, then you'd have to travel to each Gym, beat the Leader who has Pokes around Level 50-60, then go on to the next one. Now that may seem fun in theory, but imagine doing it 32 times, once for every Gym Leader after beating Kanto. Throw in Elite 4 and Champion for every Region and you do not have a game anymore. You have the longest, most boring gauntlet ever conceived. You may say, "oh, I wouldn't think it was boring, I'd love that!" but you're forgetting something.
Pokemon, for lack of a better way to put it, is for children. Now I'm not saying you can't love it when you're an adult or anything like that, but remember, the target audience is children. How many 10 year olds do you know that have the attention span to complete a game that would last around 40 hours or more? Those kids would lose interest faster than an Extremespeed attack, which would in turn, end up for bad rep for the series in its entirety. Games would be left unfinished for lack of people willing to put the man hours into the games massive story.
At most, a Pokemon game can feature two separate Regions. Any more than that, and you're pushing the audience's attention span to the breaking limit. That's why each game works best as a single Region to explore, travel across, and become Champion of."
