>> I wonder if it's a side effect of prosperity.
This is purely anecdotal evidence for your point but I'll mention it anyways.
When I was growing up, I lived on a dead end street, in a blue collar part of town. The houses were so close together, as a kid I could almost straddle between them and touch both houses. I knew every kid and their parents names, could recite every address on my block. The kids were constantly out playing sports games of all kinds, in every season. We made up games, went to the park and played baseball together. We had summer block parties and biked to the local pool to swim and chase girls. Everybody knew everybody else. We all helped each other out when things got tight. The few elderly people we had in our neighborhood got their driveways and sidewalks shoveled by us younger kids. We collected firewood for their fireplaces, we kept watch on their houses.My extended family all lived within a few blocks so I was always close with my cousins as well. I look back now and feel like it was pure Americana. When you think of the American Dream, this was the textbook definition of it.
Then in 1996, everything changed. My dad landed a new job, was suddenly making way more money than he used to. My sister went off to college and we moved to the other "wealthier" side of town. Bigger house, pool in the backyard, in a sea of larger homes. I was an only child, started high school and you know what? I didn't know anybody in my neighborhood. To this day, I couldn't tell you the names of the people who lived on either side of our house. No more sports in the streets, no more BMX racing down at the trails at the park by my house. No more hanging with the kids who would just congregate in their yards until we had enough kids to do something fun. After that first year, I struggled to make friends and for the first time in some 17 seventeen years, I actually felt alone and isolated. It lasted for at least another year when I was a junior in HS, I finally found some friends who like to skateboard, snowboard, mountain bike and play sports like I did and things got better.
But I agree, when we were living in a blue collar town? Everything felt close and you had a tight knit community. When we moved? I just felt alone and isolated. My neighbors treated us the same way. They stayed in their house and we stayed in ours. Doing better off financially was good, but I lost a lot on the way.