"Sure, I'll bite. Massive amounts of criminal fraud in the mortgage and mortgage backed securities industries, to be simplistic. To take a wider view, it was the inevitable outcome of financial services deregulation."
I've yet to see someone document convincingly the specific deregulation they think caused the recession.
There are really two questions to answer: why did we have a recession in the first place, and why is it still going on?
The reasons we've got a recession I think are simply the reasons we had a housing bubble. These are primarily the Bush-Greenspan policies attempting to alleviate the 2001 recession. Stimulus caused excessive spending and insufficient saving (i.e. high leverage), particularly on housing. This mal-investment was making people poorer, but borrowing stopped the effects from being felt. Added to which, freddie-mac and fannie-mae were tacitly underwritten by the US government, which incentivised risk taking.
There was also ineffective evaluation of risk- the ratings agency industry clearly failed to signal alarm. Extra regulation would not have helped, since the regulators were ignorant of the impending problems too. Indeed, in general, regulators didn't realise where the weak-points of the system were, again, this is understandable, since it is a global business, and immensely complicated (as any large industry will be).
Why has it gone on so long? Mal-investments haven't been done away with, and people have not been expected to meet the consequences of risk taking. Doing this would have resulted in a very sharp recession, but the present situation of a socialisation of risk and privatisation of profit. The effect is now, even businesses that did not take undue risks, and could have survived, are in trouble (see the consequences of mergers in the UK, for instance).