>>37913157I initially hoped so too, but I have come to the conclusion that this is something people shouldn't expect nor get hung up on. The concept of regional variants puts the first six regions into contention for not having regional variants and instead just having multi-national dexes, yet having Pokémon like Gastrodon and Sawsbuck and Arbok with slight changes.
I also think Alola was better designed for it because of the concept of Darwin's Finches across four islands, and the concept of Alola having a more extreme climate to justify such extreme adaptation in Pokémon we previously knew, as well as the cultural aspects of Japanese (Kanto) people living in Hawaii (Alola). No coincidence that the Alola forms were all of Kanto Pokémon, partly because of how it conveniently lined up with the 20th Anniversary marketability, and also because of the cultural and thematic inspirations of the game.
So yeah, while it seems like a good feature to have for every region, it's worth considering that the concept seemed to be designed from the ground up for Alola. It might also be worth considering that regional forms are designs and concepts that could be applied to new Pokémon entirely, or adopted from Pokémon that already exist. No point creating, say, Galarian Exeggutor, when Abomasnow already exists, and the concepts for a different Grass/Ice Pokémon could be applied to a new design entirely.