From a Wall Street Journal online article:
Economists say aging baby boomers are the biggest culprits because many are staying healthier later in life and choosing not to downsize. Some look around at the lack of smaller, less expensive homes and are loath to get into bidding wars with their children’s generation to get one.
Homeowners there are staying more than three years longer than they did in 2010. The inventory of homes for sale in Seattle has declined more than 50% over the last nine years, while home prices have risen more than 80%, according to Redfin.
Americans are staying in their homes much longer than before, creating a logjam of housing inventory off the market that helps explain why home sales have been sputtering.
Homeowners nationwide are remaining in their homes typically 13 years, five years longer than they did in 2010, according to a new analysis by real-estate brokerage Redfin. When owners don’t trade up to a larger home for a growing family or downsize when children leave, it plugs up the market for buyers coming behind them.