I wonder if this has more to do with genetic skin complexion than sun exposure. For example, I’m sure melanoma rates are very low in sub-Saharan Africa despite heavy sun exposure (although I haven’t seen data on it) 

 Genetics plays on average, a 5% role in all disease.  Skin cancers, especially the most deadly, melanoma, is diet related, or epigenetic... 

 so black people get melanoma at a maximum  of 5% lower rate than white people? I don’t think that’s right. Dark complexion plays a much larger protective role than that