>>50040781In the early games its implied that Starter Pokemon are very rare in the wild, possibly extinct (likely due to the untenable gender ratio of 9 males for every 1 female). They exist only in safe havens such as research centers or in the care of trainers.
It stands to reason that some Starters would evolve sexual characteristics meant to attract human benefactors who can protect them. Just as dogs developed infantile facial traits and neotenous behavior (to take advantage of humanity’s parenting instinct), so to have certain Starters and humanoid Pokemon (such as Gardevoir and Lopunny) developed sexual traits that appeal to humanity’s desire to reproduce and experience carnal pleasures. That’s why the chicken has tits