Hell hath no fury like a politician looking for a scapegoat. Mortgage companies that lie, steal, and encourage others to do the same are just fine until their actions lead to economic instability. Then the FBI is sent after them.
Where was the special FBI task force when all of this lying was being done openly? Why was no one concerned then? This is not a case of sneaky documents being signed in the Cayman Islands. Mortgage companies competed for business by creating "liar loans" that required no income verification.
Now that there is political pressure from someone in Congress, the FBI springs into action. Where were they before? Why is it a crime worthy of their focus at this time, and not when the practice started to happen? And why does it take a crisis for anyone in Congress to decide there's a problem?
The financial interests of the mortgage companies put pressure on Congress such that they didn't want to see an obvious problem. Mortgage companies donate to political campaigns, after all. And they hire constituents who vote for politicians. So Congress was content to turn a blind eye towards a systemic problem.
But wait! The entire system is melting down! I might get thrown out of office! Let's get an investigation going so people associate me with vengeance instead of greed.
And that delivers us to where we are today: hunting down the mortgage lenders and giving the cowardly national leaders a pass.