There are far more diabetic and pre-diabetic people than there are people with Crohn's and gluten allergies. Yet "gluten-free" is a trend and "low-glycemic" is rare.
It is due to the invention of the "food-allergy specialist" and other non-certified variants. If you are getting diagnosis from somebody who doesn't have '#allergist' in their title, they aren't a certified-by-the-AMA allergist, which requires ongoing education.
Ask for credentials.