The proximate answer for the US is that a decline in lending standards helped people buy houses at ever-increasing prices before 2006. Freer lending meant that people were freer to bid up prices of homes to ridiculous levels.
对美国来说，住房价格下跌的近因是，在2006年之前，贷款标准的降低使人们在房价不断上涨的情况下买房。更宽松的贷款意味着人们可以更容易地将房价推高到荒谬的水平。简陋的小房子都卖到了一百万美元一套。