Why use a rural image in a policy brief about "the American middle class"?

That's what the Brookings Institute did here. 

But I can't find any significant rural angle in Brookings analysis of the "seven reasons to worry about the American middle class."  They do use the word "rural" twice under the heading "Place Matters More than Ever."  Here's an excerpt (emphasis added): 

Alongside the diverging destinies of individuals is a great divergence in the prosperity of whole communities and regions of the country. Employment and economic growth is far from consistent from one metropolitan or rural area to the next. Because various parts of the country are home to different industries and occupations, trade and technology have had differential impacts by region. Employment rates have, for example, fallen most dramatically in the nation’s rural areas, though there are still more non-working men in cities than in the heartland. 

Our Brookings colleagues Mark Muro and Jacob Whiton find that the largest metropolitan areas have accounted for the vast majority of the nation’s population, employment, and output growth since 2010. For the first time, the rural population is actually shrinking. This, alongside the declining role of manufacturing and mining, means that employment growth, an important contributor to overall economic growth, is waning in many parts of the country.