It’s a multifaceted issue thats predominantly socioeconomic. Urban areas are less likely to have greenery, brick and asphalt and concrete make the areas much much hotter than an area with green coverage or even just dirt. High rates of obesity and heart disease, poorer quality food resources make it difficult for the body to adapt.
In some places, GOP policy has made it legal for business to deny water breaks, and if we’re going based solely on statistical distribution of labor per group, blacks have higher rates of outside/physical jobs, another systematic and socioeconomic issue.
The third issue is that in these areas, health care is often poorer quality/under funded, even when they do get to the hospital/ER/urgent care facility, they die at higher rates of similar diseases than other areas.