And why is that?

Excessive mobility, loss of human scale, community and etiquette and common mores, and ethnic diversity imposed from above.

The Loneliness of the Anonymous Neighbor By CASEY CHALK
Increasingly we don't know, care, or trust the people who live near us.

This essay has a decent start and middle but ends with some sort of "Christian posturing."

The anonymous neighbor, like so many other tokens of our time—the teenager whose closest friends are virtual, the single adult male spewing vitriol on the internet—is something we must resist if we want to live fully human lives. It may sound cliché, but neighborliness is one of the most American of qualities.

Good anecdotes to illustrate the problem, but no useful analysis or understanding of the causes.