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That's a mischaracterization of why the technique of palette swapping exists.I blame Shiny Pokémon for popularizing recolored Mons.
Edit: Also, to quote Abridged!Godwin: https://www.youtube.com/watch?v=P6VqHCvdg9I&t=265s
Sprites/models are expensive, especially the more unique a design is, and disk/screen space was a serious concern because of console limitations. Therefore, it was considered cost efficient to reuse assets whenever possible to insure the player has enemies that are able them power-wise.
It's not like this isn't reflective of real life zoology either since being descended from a common ancestor, members of closely related biological groups (like a family or genus) often closely resemble each other in basic body plan, but have adapted to various environments and ecological niches through changes in color, size, diet, and behavior with the most notable examples being Darwin's Finches and the countless species of beetle across the world to the point there is a famous quote that goes "If there is a creator, he has an inordinate fondness for beetles."
Also, regional variants would be a more accurate Pokémon analogue to how palette swaps are traditionally used and that didn't become a thing until the 2010s.