Life expectancy doesn’t always give the whole picture. For example, in my graph, there are times where China’s life expectancy is rising very rapidly, but it was still considerably lower than that of other countries. It’s necessary to analyze what policies lead to what results and what the reasons are for the success or failure of a given political project or policy.
I haven’t studied South Korea’s policies and material conditions closely enough to offer much of an informed analysis, as the world is a very big place. You could always make a thread about it on c/askchapo or something.