I'm going to draw the obvious conclusion that most of the models were built on the premises of mediocristan, when in fact the world they were modeling lived in extremistan.
The thing is that quants who come up with models showing large amounts of risk to otherwise profitable investments aren't as popular as ones who say everything is just fine. So there is a clear incentive for models to be optimistic.
I thought this was a great analogy to express your conclusion:
"It was like a weather forecaster in Houston last weekend talking about the onset of Hurricane Ike by giving the average wind speed for the previous month."
The thing is that quants who come up with models showing large amounts of risk to otherwise profitable investments aren't as popular as ones who say everything is just fine. So there is a clear incentive for models to be optimistic.