My observation is that it is the ease of seeing people that leads to loneliness. The midlife crowd are off driving their kids to a different sporting event, or what have you, every day of the week. It is so easy to see people that they never stop to see the same person twice, so to speak, and thus the repeated engagement required to form friendships isn't likely to happen.

If we look back at older generations, who notably lived in far less density than what is common today, they by and large had less trouble with loneliness as the difficulty in seeing people from limited transportation availability meant that they could only ever get to know their closest neighbours, which meant that is who they saw over and over, and that lead to friendship.

80% of the US lives in urban areas. Surely at least those should find some friends nearby?