Interest isn't the only cost to own a home.
http://www.nytimes.com/interactive/business/buy-rent-calcula...
http://www.nytimes.com/interactive/business/buy-rent-calcula...
Appreciation in the Bay Area and other denser areas have seen prices grow at more than inflation, which is probably attributable to restrictive zoning limiting supply over the long term. I agree that's not sustainable economically, socially, and hopefully politically.