Either it's portion sizes, diet, or genetics. Or something else. But so many population risk factors are higher for South Asians at comparable stages of their life (same age, BMI - adjusted down, etc) that it would be a mistake to assume based on first principles.
Roti, paratha, bhatia come to mind. It is sometimes easy to think in South India urud daal is only used for idli / dosa but the south definitely consumes its fair share of other bread varieties
North Indian - daal, roti, 1-2 vegetable sides, yogurt South Indian - sambar, idli (rice, urud daal), other urud daal based breads