Shirley, that is what we are all asking.
My opinion is that many people have sold because of distressed situations. There are those who would like to sell but don't have the equity and/or don't want to compete with the multiple offers on the buy side. There are those who are content and have no desire to sell.
Those who are selling either have to due to financial reasons, job relocation, and change in family. Move up and move down. There are those who have passed away and the trust or family are selling. The rest of the people, like Allyson said, are waiting.
There are some great reasons for sellers to consider todays market which they may not be aware of. If their property is a condo, many of those condo FHA certifications will be expiring soon. Two recent ones I looked up expire in September of this year. Buyers interest rates are low and the FHA hasn't increased to 5% yet so those make for good buyers. Sellers who may have a huge capital gain may be effected in 2013 when I hear that may be increased by 3.5%. That could be a significant hit to some sellers. Inventory being low there are fewer competition for the sellers. Meaning the demand will be that much more of a benefit to the Sellers.
Have an amazing day.