[1] The availability of a deficiency judgment depends on whether the lender has a recourse or nonrecourse loan, which is largely a matter of state law.
In some jurisdictions, the original loan(s) obtained to purchase property is/are non-recourse, but subsequent refinancing of a first mortgage and/or acquisition of a 2nd (3rd, etc.)
States that follow the title (trust-deed) theory of mortgages typically allow non-judicial foreclosure procedures, which are fast, but do not allow deficiency judgments.
States that follow the lien theory of mortgages require judiciary foreclosure procedures, but allow deficiency judgments against the debtor, although some states have narrowed the time periods to seek a deficiency judgment.
[3] In 2014 Geoff Walsh, a staff attorney with the U.S. National Consumer Law Center, said on NPR that the United States is "seeing an uptick" in the pursuit of deficiency claims, because technological developments have enabled large debt-buying institutions and mortgage insurers to more easily pursue former borrowers, who often don't know their legal rights.