Why do people develop hemochromatosis?

It's in the genes. In hereditary (= inherited from parents) hemochromatosis, too much iron is absorbed by the gut & deposits in tissues. Liver, heart, other damage can result. It is autosomal recessive: both parents must carry the gene & not all offspring will be affected. Secondary (= due to other causes) hemochromatosis can occur with certain types of hemolytic anemia (red blood cells bursting, releasing iron).