"In an economically divided America, Walmart has tried to sell not only to shoppers looking for extreme discounts, but also to shoppers with higher incomes seeking higher-quality items.
Walmart has been working to increase its sales to more affluent customers for years, especially in e-commerce."
https://beta.finance.yahoo.com/news/walmarts-latest-move-confirms-death-173551843.html
There is a strong bias in the media and academia to studying metro areas. There are obvious reasons for that (you need a population to study, you need a population to buy your publication, etc) and less obvious reasons (cultural blinders because most media companies and research universities are in metro areas).
All of that to say that I'd like to see the study that covers 229 rural areas and see how the middle class is doing there. I bet there's been a decrease in middle class population in 223 of those areas.
I rest my case