Final answer:
The main reason why the US lags behind in measures of population health is the lack of universal healthcare coverage.
Step-by-step explanation:
The main reason why the US lags behind other developed nations in measures of population health is the lack of universal healthcare coverage.
While the US is one of the wealthiest nations, it still struggles to provide affordable and accessible healthcare to all its citizens.
This leads to disparities in health outcomes, with higher rates of infant mortality and lower life expectancy compared to other developed countries.