Embolding mine.
I plussed your post for pointing this out, but frankly, people who have lived their entire lives in dense populations have a difficult time understanding that dynamic. I think you just have to live it to understand. Social psychology is a remarkable thing.
I was raised in a urban/suburban environment, then moved into a wilderness environment that, over the course of my lifetime here, grew into a rural, then suburban environment. I have always been a social kind of guy personally, but anti-social in ideology (very weird, I know). I want to know my neighbors, endeavor to enjoy their company, go out of my way to be helpful and kind. That is much easier in a rural atmosphere, but even in the crowded suburban landscape of Orange County, California, I have found that most people want to be good neighbors and socialize to some extent, even though there are widely variable racial and ethnic lines to cross.
But the bottom line is that smaller populations are very easy to be neighborly. The entire state of Alaska has a resident population equal to that of the city of Long Beach, California. The current governor is a fellow parishioner at the church I attend. I've personally known previous governors, U.S. Senators, our Congressman, and local politicians or their family members. Everybody knows everybody. This just doesn't happen in giant populations of millions upon millions of people.
Edited to add:
The basic human social unit is the family. This is likely the unit the Neanderthals lived in. From there, the family bonds to other families into a community. From the community level, increased human density requires increasing social effort to co-exist peacefully and efficiently. Thus, family and neighborhood tend to form the greatest emotional bond in a persons soul.