I wonder if it’s related to lower smoking rates.
(graph from Centers for Disease Control)
For details and further conjecture, read the New York Times article:
“Something strange is going on in medicine. Major diseases, like colon cancer, dementia and heart disease, are waning in wealthy countries, and improved diagnosis and treatment cannot fully explain it.
Scientists marvel at this good news, a medical mystery of the best sort and one that is often overlooked as advocacy groups emphasize the toll of diseases and the need for more funds. Still, many are puzzled.”