It's probably demographics to a large degree. A lot of people have families and family-related activities and they largely drop out of random socialization.
Sure, but having additional responsibilities when you have a family is not a new phenomenon created in the last 30 years.
I'm not convinced that shifting away from general social activities is an especially recent phenomenon though it may be true that just leaving the kids at home with a babysitter/nanny/older relative when you went out may have been more common in the past.