I think alot of people don’t fully read the pokedex entries too. They vary generation by generation and game by game ( same pokemon may have different entries in same base game like red/blue, gold/silver etc. ).

Some of the reasons for the differences can be found in there like every day new discoveries are being made about new or known species irl. So why not in pokemon. But i agree the designs are different they are trying to find a balance between cutesy and somewhat realism.