I wonder if "life expectancy" is really such a useful metric, since it aggregates so many different things together. It's kind of like measuring "aggregate years of human life lived".
It's still useful because it provides some information. Specifically, a change in life expectancy, or a change in the rate of change in life expectancy (as here) means something. We just don't necessarily know what that something is without further study.
It leads to a lot of misunderstandings. For example, lower life expectancy throughout history is far more attributable to higher infant mortality than to adults dying young. But people think everybody died at 45.
