Inside the seller's market for houses

We told you last week how hard it would be to find a home to buy this spring. The AP's Alex Veiga explains why the nation's "supply of homes for sale hasn't been this thin in nearly 20 years" (especially those affordable for first-time buyers):

• "Since 2008, the average time homeowners have stayed in their houses before selling has doubled to nearly eight years."
• "Some who had locked in ultra-low fixed mortgage rates may be reluctant to take on a new loan at a higher rate. Others may wish to sell but can't because they own one of the 3.2 million homes worth less than what's owed on their mortgage."
• "Some homeowners own other properties they rent out and have little incentive to give up the steady rental income, especially while they're also benefiting from rising home values."
• "Investors, who typically keep properties for disproportionately long periods, own a larger share of houses."
• "Though the pace of building has been rising, it has yet to make up for years of sluggish construction growth that followed the housing bust."

What it means: "The homes that are on the market are less affordable to a growing proportion of the population."