Yes, perhaps I've explained this poorly. My apologies.
Biata are the intellectual property of Mike V. They were designed by Heidi. The Celestial allergy is considered core to the race by both the designer and the IP owner. Because Biata are unique to Alliance, that IP has actual legal value in a way that many fantasy tropes do not. Remember when Underworld came out and White Wolf games got mad and threatened litigation? They never actually sued because vampires and werewolves are common domain concepts, nobody owns those. The Biata concept, on the other hand, is unique. That uniqueness is protected to a degree by keeping the race consistent.
Add to all that that Mike has no interest in changing the race and you have a pretty compelling case for leaving it as is, from my perspective.