I've been hearing that "young people don't have families" explanation since all my friends were young people who didn't have families, but the long-promised exodus to the suburbs continues not to materialize. If anything, we've all been clustering more and more closely together. The people with kids want to be around other people with kids, but we all want to be around our friends. If people can't afford a house on their own, they're far more likely to find another family and set up a co-housing arrangement than to exile themselves to the suburbs.