Because modifying the vanilla armors to fit it would be a nightmare. Be thankful for the costume and keep it at that
Because race suggestions generally need a very high level of detail. For a legitimate suggestions, you need to be aiming for paragraphs. History, society, culture, biology, technology, etc. A thread title and rhetorical question is nothing. And there's also the matter of sprites, as Darklight mentioned. All playable races currently use the same spriteset, for the sake of easy implementation and the fact that all races can use all equipment (namely armor).
I will think of this as a modding and story writing challenge, so COME AT ME. I really like mods and alpacas, so like you said, why not? And I can get most of the alpaca sprites from the game files anyways.
I just made the Froggs as a part my race mod "The Canids Race Expansion". Here are a few samples of the sprites. The model can be customized in the belly, skin, and eyes. I have sprites for shirts pants and hats that go on the Froggs. These are some samples of the Frogg clothes. It overlaps the coat on the character sprite. These are sprites for an outfit that goes under the Frogg's iconic coat. It took me several days to get this all perfect; and I am still no where near done. I wanted to show this hoping that it would help you know where you are going with this @Uriko .
Thank you for this piece of information. Did you create this yourself or manage to grab some of the npc assets to start you off? I'm hoping to be able to take the alpaca npc assets or the armor set's assets to help me start off with the appearance at the very least.
I created all of this from scratch. The sprites, of coarse, are all taken directly from the Frogg costume. There is a mod that will give you a head start Skittle's Template Race Mod.