Look up the difference between “recourse” and “non-recourse” states. In a non-recourse state, the mortgage lender gets the house in a foreclosure, and there is no other recourse available (like suing for the remaining debt). Only 12 states are non-recourse, but some of the big players in the 2008 financial crash are among them (California, Arizona, Texas).
I wasn't aware of the divide between recourse and non-recourse states. Google tells me: <<Alaska, Arizona, California, Connecticut, Idaho, Minnesota, North Carolina, North Dakota, Oregon, Texas (sometimes), Utah, Washington>>