>>38693254https://www.pokemon.com/us/pokemon-news/creator-profile-the-creators-of-pikachu/>“I created the designs for Bulbasaur, Charmander, and Squirtle by working backward from their final forms. I wanted people to be surprised when it evolved into Charizard, so I designed the original Charmander in such a way that Charizard would be unimaginable.”I remembered the quote wrong but it's along the same lines - they want the final forms of starters to be a surprise you wouldn't expect which is pretty understandable. I'd assume they kept a similar mindset for all future starters, except perhaps Gen 2.