1. Force to sell due to medicare or other end of life expenses (you can not have any assets if you need full time nursing care paid for by medicare)
2. the "Reverse mortgage" people fall for.
3. Baby Boomers, a Single Asset split 5-8 ways does not go far
4. the houses owned really were not that good. My Grandparents owned their home, bought it right after WWII, the house was a small 2 bed 1 bath they raised 4 kids in... It is still in the family but it is out-dated by modern standards.
that is 4, I am sure there are others