Interest rates are still low enough for folks to afford more house than they need, and builders are obliging them.
To buy the median house at $321,100, with 100% financing at 4%/30 years, the monthly principal and interest comes out to $1,532.98. Add between $600 and $1,000 a month for property taxes and insurance. The family income required for the top of that scale is about $108,550 based on 28% of income. Well off, yes, but wealthy? No. And in some loan programs (40% total of all debt permitted) a low-debt family can buy that much house with a considerably lower income. With zero debt about $76,000.