Never mind. It was more complicated than I thought.
There was somewhere around 1 to 2 $trillion of house value in the bubble (out of perhaps $10 Tn total, not including commercial property), and tied to that was a disproportionate amount of uncertainty since all the securitized mortgages mixed them together and then the CDS chains of insurance created multipliers. Now in theory each mortgage sums to one when you count up all the pieces and match buyers to sellers along the chain.
The problem is, they don't match up. Pieces of the chain fail or are not synchronized because of lack of liquidity and so the contractual values get claimed at several points in the chain and not satisfied. Before the chains can work properly, they are in pieces and you have 10s of $Tn of these failures dangling in commerce-space. And it is not helped by all the players independently trying to claim what they can and refuse what they can. If someone claiming on you goes bankrupt then their ability to press the claim is deferred or even vanishes, so there are profits to be had by delaying, and meanwhile the same logic is applied to your claims. Sauve qui peut.
Cool. Financial wizardry intended to reduce risk instead, because the implementation is faulty, has ended up greatly magnifying the destruction.
In the end, money ends up in very different places than where it starts, somewhat randomly.