What this and the sibling comment ignore is home construction. Without construction (or without cost effective construction) home prices have zero incentive to fall. Home owners will trade homes between themselves at 'inflated' prices. If you can not produce a home cheaper than an extant, equivalently sized home then prices effectively have a floor.

National average construction cost per square foot is $160. $160 * 2000 square feet is $320,000 sans the land which we can assume is 25% the cost of the home constructed on it. So we've magically hit the $400k number.

The only way home prices 'decline' is with population decline, coercion, a recession, or significant regulatory, cultural, and financial shifts.