>>39696109The way people talk about them is very telling. Older mons are usually thought about as species of monsters/animals. You can imagine them having different personalities depending on the trainer. They are a blank slate personality-wise, beyond some instincts inherent to their species (like real life WILD animals generally have a set personality/behavior we expect from them). So you can buy that there's a whole species of them and each one is an unique individual.
These new humanoid mons are literal cartoon characters. Rather than feeling like you are training a huge lion or elephant, you feel like you're training a weird ass mute man-cat with a human personality, intelligence mindset. You don't feel comfortable cleaning up their shit, petting them or letting them see you naked.
While the early gens had humanoid mons, they were rare, meant to be off-putting, not shoved in your face and usually evolved from equally weird humanoids. You never had situations like a fucking STARTER being a humanoid and evolving from a perfectly normal animal. Blaziken started that shit. Not only was "he" (note how I think of "him" as a character and not a species) humanoid in appearance, he also had human intelligence and pride and shit. Creepy. He ruined Torchic.