My experience is not like that at all. On the contrary, people I know became less and less concerned with keeping an extended social circle and retreated to family.

This retreat in many cases has a lot to do with the refusal to put up with other's annoying behaviour. Family is no peace oasis either, but it's more difficult to defect from it :)

I return to my hometown for holidays and see this effect every year. There are still big groups of acquitances, but they're more homogeneus than what they used to be. I believe there's a big pressure when you're young to have a lot of friends and to fit in. When older we become grumpier and less tolerant of neighbour's faults.