I think isolation is great if you have everything going great in your life: great job, great apartment both close to a city center where you can go out to have fun and meet other people, and have great health.
The problem is that when economy or your health gets worse, you start to depend on your family and friends more. In a culture where isolation is norm, I can imagine that it takes lot of time and effort to reverse the trend.
Second up is economics. The US economy has been hollowed out. Unless you are in a few industries (tech, finance, upper management, high end sales and marketing, doctors, some lawyers) you are looking at dead end jobs with low pay and poor benefits. High earners are not immune either. Most high earning jobs are concentrated in a few large cities with consequentially outrageous real estate costs. A lot of your earnings are eaten by the "law of rent."
There are other causes too but I think those are the largest.