The New York Times says the most important reason for the shortage of affordable places to live is that local governments are preventing construction

Americans Need More Neighbors: A big idea in Minneapolis points the way for other cities desperately in need of housing. Excerpts:

"Housing is one area of American life where government really is the problem. The United States is suffering from an acute shortage of affordable places to live, particularly in the urban areas where economic opportunity increasingly is concentrated. And perhaps the most important reason is that local governments are preventing construction."

"Increasing the supply of urban housing would help to address a number of the problems plaguing the United States. Construction could increase economic growth and create blue-collar jobs. Allowing more people to live in cities could mitigate inequality and reduce carbon emissions. Yet in most places, housing construction remains wildly unpopular. People who think of themselves as progressives, environmentalists and egalitarians fight fiercely against urban development, complaining about traffic and shadows and the sanctity of lawns."

"People should be free to live in a prairie-style house on a quarter-acre lot in the middle of Minneapolis, so long as they can afford the land and taxes. But zoning subsidizes that extravagance by prohibiting better, more concentrated use of the land. It allows people to own homes they could not afford if the same land could be used for an apartment building. It is a huge entitlement program for the benefit of the most entitled residents.

The loose fabric of single-family neighborhoods drives up the cost of housing by limiting the supply of available units. It contributes to climate change, by necessitating sprawl and long commutes. It constrains the economic potential of cities by limiting growth."

"The affordable housing crisis cannot be solved by new construction alone, at least not in the short term. Governments need to provide subsidized housing for people who cannot afford market-rate housing. But advocates for affordable housing should be jumping up and down and screaming for the construction of more high-end apartment buildings to ease demand for existing homes."

"Market-rate construction also can help to reduce the need for public housing subsidies in the longer term. Today’s market-rate apartments will gradually become more affordable, just as new cars become used cars. The price of the average rental unit declines by 2.5 percent a year, adjusting for inflation, according to a 2014 study."