This article claims that avoiding "Mark to Market" (FASB 157) reporting is to blame.
It was quite the opposite in 2007 and 2008, when marking to markets that disappeared caused a chain reaction of asset liquidations to keep up with statutory capital requirements as values plummetted for no reason other than market makers voting "present."
I'd post this comment on that site but I'm not going to bother with registering, etc. And as "mish" seems to think it's an "excellent" point, I'll take issue with it right here.
It may have contributed to the collapse in 2007, but you could say it was also just accelerating the move to real market value. That was painful, but necessary to clear out bad assets. Now you have banks sitting on billions of dollars of those bad assets that need to be liquidated before a recovery can really happen.