The home was reportedly listed as a power of sale, which differs from a regular home sale. The clause is usually written into a mortgage note that authorizes the mortgagee to sell their property in the event of default to repay the mortgage debt.
As a result, the lender forces a sale on the public market and gets all the funds owed to them, while the current owner gets to keep any excess profit. In a foreclosure scenario, the lender usually takes ownership and gets to keep all the profits from the sale.
I bet the former owners initially made an $800,000 down payment. The timeline of price drops was rapid, just over a matter of months, so I'd guess the low selling point was probably pushed through by the bank trying to recover the money they lent as quickly as possible.
Here's some pics: https://2.bp.blogspot.com/-yjf73vy_VRo/T6rqS_Yec_I/AAAAAAAAAFQ/nAKPcFeo87w/s1600/durendal.jpg
https://www.ancient-origins.net/sites/default/files/embedded-stone-in-Rocamadour.jpg