In San Francisco, a household making $78,840 a year can top out buying a home worth about $409,000. 24 percent of the homes for sale in the area were below that threshold last October. Now it’s just 14 percent. In fact, in every one of those 10 metros, a smaller share of homes are considered affordable now to the middle class than last year.

The same trend is true even in those metros where the vast majority of housing is accessible on a local median income…