Only 10% of new homes now sell for less than $300,000. Two years ago, a third did. It’s not just because of the pandemic.

Homeownership became out of reach for millions of Americans following the recent boom in home prices. Lower-income families have been hit especially hard, with the share of new homes selling for under $300,000 plummeting to 10% from 35% in just two years.

A number of factors, including more than a decade of limited homebuilding, a sudden and sharp rise in demand related to demographics, seriously low mortgage interest rates, and lifestyle changes, and surging homebuilding costs caused by pandemic disruptions are all partly…