the devs don't want all the sprites to be super different from each other or it could create a bunch of complexities (like the block to player size ratio), so all the races are the same height, are of similar widths and are all bipedal. that limits the choices of how to make them look different down to very details.
yes, the race suggestions being made to have characteristics the same as other animals we know exist on Earth is a bit annoying, but it's also a very natural thing to do. i don't want every race in starbound to be something complete weird and out the ordinary, and if that's how you are then you're searching for too much originality.