Overthinking it.
We've had Goblins, Kobolds, Sylph's, and Moogles all be a part of MSQ as friendlies. Especially the post-moogle. Idyllshire has goblins everywhere. A similar thing exists with the Kojin.
The only reason why X is not a playable race, despite there being models in the game for, is that they don't have customization. All the beast tribes clearly have some variation on "caster, healer, lancer, ranger" but you'll notice the only thing that makes them that is their weapon. They have no other gear.
Final Fantasy in general, I'd say that it's not out of place to have playable characters that aren't fully human (see FFIX) but it would be out of place to have races that aren't "human enough"
In the context of FFXIV, I think they likely initially wanted something more like what the Lupin are, before the Au Ra became final, but decided that "yet another miqo'te" wouldn't be different enough, and the customization would be too complicated.
Like, there's exactly two models for the Lupin seen thus far, the villager, and the imperial. They have their own "random enemy NPC" just like the bandit/pirate camps in every area. The playable-races all have variety (though the majority of NPC Roe are green.)
