Fascinating research findings of “Social Connectedness: Measurement, Determinants, and Effects”

They plotted U.S county-level binned scatterplots using the share of friends living within 100 miles and a number of socioeconomic outcomes.

The conclusion: Counties where people have less concentrated social networks tend to have better socio-economic outcomes: on average, they have higher income, higher education, higher life expectancy and lower teenage birth rate. Even though the causality relationship has not been researched in detail, there is a clear correlation between a social network and socioeconomic outcomes.
What could be the reasons behind the phenomenon…