Because the market is not being allowed to correct it. We still have the Federal Reserve keeping interest rates down. We still have government bailouts saving companies that make bad loans. Credit card companies still feel safe to lend money like water, because if you default on your credit cards, the government will repay what you owe.
Its like the old analogy I think I have posted here before. If you have a rich uncle who owns a casino, and offers to repay you any money you lose, how much are you going to gamble? Even if you lose everything you have, you will not learn your lesson, because your uncle just pays back what you lost, and you can bet again.
A marker correction would involve Fanny Mae and Freddie Mac either going out of business, or correcting their bad lending policies. Since the first isn't going to happen because the government will always bail them out, they have no reason to do the second.
And remember, those two lending institutions were founded during the Great Depression as part of FDR's New Deal, in order to provide loans to poor people who the other banks considered bad risks. And what are they being criticized for now? Lending money to people who are bad risks.
We are now living the in future that economists warned Keynes about, but he dismissed with "In the long run we are all dead."
"The final outcome of the credit expansion is general impoverishment."
Mises - Human Action, p. 562; p. 564