If you come from a family with a history of dying younger, experiencing higher healthcare costs, or posessing some debilitating illness than it would make sense that your lifetime earnings / final net worth would be lower.

What I'm saying is that the disparity between rich and poor on life expectancy is INCREASING, not just that it exists. (I'm also not sure if they use income or net worth.)

The second thing I'd hypothesize is that a large part of this is the decreasing economic power of rural areas. Those places with less available health care have been particularly economically weak as of late.

Could be. I'd imagine there's a ton of complicated dynamics including race, urban/rural, and much more. So yeah, could definitely be this and I think this is a much better way of looking at it rather than as one life expectancy number for the country that either goes up or down.