I'm certain if you looked at the eating habits of these people you would find a diet high in refined sugars and junk food which not only affects their teeth, but also predisposes them to diabetes.
I happened once to visit with a man who was a route driver for a company that supplied snack (i.e. junk)foods to gas stations and convenience stores. His route encompassed one of our local Indian reservations and he boasted that his sales of snack items were the highest in a three state region solely because of sales on the reservation.
Your genes predispose you to Type II diabetes, not the consumption of sugar or other carbohydrates. 95% of the population do not have those genes so they can eat their fill of candy if they wish.
Their teeth will still rot!