Why did Pokémon Black and White have no old Pokémon?

Boot up Pokémon Black or White and the grass holds a shock for anyone who had played since 1996: nothing is familiar. Until the National Pokédex arrives after the story, Unova contains only its own 156 new species. No Zubat in the caves, no Geodude on the cliffs, no Magikarp in the water. The developers spoke openly about the intent: a completely fresh experience for new and old trainers alike, in which a veteran's fifteen years of knowledge were worth no more than a beginner's curiosity.

The fiction carries the design. Unova is framed as a region far away from the four that came before, across an ocean, so its wildlife is its own. The 156 newcomers were built to fill the old jobs with new faces, the regional bird, the early rodent, the cave bat's replacement, so the game plays like a first generation that happens to be the fifth. Even the family tree was closed: none of the 156 evolves from, or into, any Pokémon from an earlier generation.

It was a one-generation experiment, and the games own that too. The moment the story ends, the gates open: the National Pokédex arrives, eastern Unova fills with older species, and transfers from the Generation IV games begin. Black 2 and White 2, two years later, reversed the policy entirely, stocking Unova with 300 species from the first route.

For the Library, the empty grass is the point of the artefact. Black and White are the only core games that tried to make their own audience strangers again, and the gamble is preserved in every Unova cartridge: a Pokémon game that begins, on purpose, with no Pokémon you know.