I'm not saying weight is not a problem, I come from a black family where unhealthy diets are a tradition (but that leads back to the fact that traditional african american diets come from the slave food which was unhealthy but taken in as cultural meals, much longer discussion there), but that does not mean that taking out weight in this discussion solves all or even most of the issues at hand.
As well using your same logic, why do Asians who typically have a lower BMI than white individuals have higher incidences of Diabetes? It's not one size fits all
https://health.usnews.com/wellness/articles/2016-03-11/asian...