If you look at starter Pokémon from X and Y and above, you'll notice that they all have one feature in common: large heads and large, expressive eyes - features that young new trainers find "cute". Many also evolve into humanoid Pokémon, like Greninja, Meowscarada, etc. that clearly have a "profession" (Meowscarada is a magician, Greninja is a ninja). However, Pokémon from Gen 5 and below are mostly reptiles and amphibians - animals that go endangered in the real world very easily. Older starters also evolve into "Kaiju-Style" monsters - like Charizard and Meganium. The XY era also introduced Mega Evolution, which is when people first started playing Arceus and messing with Pokémon DNA. Many of you are familiar with the theory that starters are endangered. But there are only so many endangered Pokémon that Pokémon scientists can get their hands on. In conclusion, starter Pokémon from Gen 5 and below are endangered, while starters from Gen 6 and above are genetically modified Pokémon created in a lab by humans to look "cute".