Median house size is > 2000 sq ft, so common people are buying large houses. They're certainly not out of reach. The US has (except maybe Australia) the larges

Median house size is > 2000 sq ft, so common people are buying large houses. They're certainly not out of reach. The US has (except maybe Australia) the largest median house sizes on the planet. Home ownership has bounced between 63% and 69% for over 50 years, and is currently rising again. What force makes a smaller home sustainable but a larger one not sustainable?