Re:
This isn't 100% in the US, though it is declining overall. Some families do have small attached units for their parents. However, AT SOME POINT, the parents health will decline to a point the children cannot care for them. This is a reality of how life is lived in the US. We match expenses to income, nearly, then barely save enough for the ourselves, let alone, the parents or kids. With that in mind, few families can transition to caring for parents. I do many families that parental units attached, and Long-Term Care as the safety net IF and WHEN the parents are sick enough to require such care.
It's an UN-reality now. My grandmother on my father's side said if "anyone wants her money, they better let her live with them", but it's very degrading. At some point, a parent may have alzheimer's, incontinence, barely be able to walk, to dress, to eat, or have some moments of dimensia. Do you want such drama around young children? Do you want to be dipering your parent's? Can you afford to restructure your home to be disabled friendly? Sure, if your parents are in their bristling 60-80's (about), you can have them move in with you, but as the population ages, people are not ABLE to care for parents in a way that would be comfortable AND medically feasible.
My mother's a nurse, and she can't POSSIBLY come home and THEN care for her parents, too. It was sad enough she acted as liason for our grandparents, since most of the nurses/doctors weren't that good as our relatives were passing, and she helped decipher what they were saying and/or needing.
It was the way it was, because both parents weren't working, they didn't live long enough to develop SERIOUS medical issues that require professional care, and they had MORE people living at home longer that could pitch in with various chores. I have visited/dated Asian families, and they are the last race that is adhering to these 'old ways'. One particular girl had some 5 or 6 siblings, and 4 of them were with kids and a wife/girlfriend. ALL of them lived at home, so there were about 15-20 people. Each person had a specific talent that was valuable to the homestead. One brother/son was a carpenter, one a mechanic, one a regular worker, the mother a cook, the daughters/daughters-in-law watched the kids, transported them around, etc.
It begins and ends with family values and changing demographics. We're living longer, get more serious illnesses that don't necessarily kill us, only disable us, there are less kids, and most of these kids cannot afford the time off from work. And adding to the mounting pressure are high divorce rates. It's not all women, but they might not help the situation either.
A-Unit
Sounds harsh but thats truth