I'll link to a Matt Yglesias post which links to a NYTimes article on the Obama administrations slow and small efforts on the housing front.
A sentence here: "But none of that explains why they were so slow to spend the money that they had that was earmarked for housing."
As is discussed in the article, the policy choices were bad: helping borrowers who were under water meant in the eyes of many, including me, helping people who had gambled and lost. But another factor is, I think, the lack of the appropriate bureaucratic infrastructure. The Feds don't deal directly with homeowners and borrowers, they deal with mortgage lenders and bankers. So if Geithner, Obama, and Summers decided they wanted to do something, the existing bureaucracy wasn't set up to analyze alternatives and propose machinery which could carry out the policy.
This is just another instance of my "we have a weak government" meme.