[CORed]

For most of the history of humankind, we have lived on the edge of starvation. This means that eating any kind of high calorie food when the opportunity presented itself was a survival enhancing move. Also, putting on a nice load of fat provides you with "famine insurance". Constantly pigging out on high-calorie, but otherwise now nutrient food isn't good for you, but that's not an opportunity most people had, until fairly recently in human history.

Another thing to consider: Longevity isn't really something that's selected for all that strongly. If you live long enough to have some kids and raise them to adulthood (40-60), there's not much benefit, evolutionarily speaking to living any longer.