>>34319512Unlike other regions, where the new Pokemon were "always there since the beginning," Johto was designed as an instance of the 3 year gap between Kanto and Johto giving time for new species of Pokemon to surface in both regions either through migration, being introduced to the region by humans, or other such means, although they primarily showed up in Johto.
Not only that, Johto's literally next door to Kanto to a point where they share the same Victory Road and Pokemon League, so it's no surprise Kanto Pokemon took up the vast majority of its fauna.
This was pretty much done purely to point out how much GSC were actual "sequels" to the previous titles, whereas the ideology of future games was that they were standalone titles that needed little to no knowledge of past releases in order to be familiar with the game's settings, story and other stuff like that.
