'Zombie offices' spell trouble for some banks
nytimes.com
nytimes.com
The theory posited at the time is that this would have triggered collateralised debt obligations which would have resulted in a cascading spiral of CDO triggers which would have revealed that each dollar of commercial real estate had been used to generate 5000 dollars of 'securitized' debt, or some other ludicrous figure.
There's a pretty famous infographic somewhere which shows the ridiculous scale of the CDO problem.
It was illegal. It was illegal for over half a century. From the get depression onwards when it previously caused huge problems. And then a group of people started chanting about 'deregulation' and how much money they could make and yet again people feel for it and ignored all the lessons learned lay time people for greedy and started asking for lax oversight and rules for their financial markets. And we'll keep having examples of lessons to re-learn until we put the same regulations back that prevented this.