The reasons go directly to regulatory differences that should interest Americans. Take nonrecourse mortgage loans. When Australians [and NZers] borrow money to buy a house, they know that if they default and the mortgaged property doesn't cover the debt, they will be responsible for the shortfall. And the lender will chase them for it. It's a neat way of reminding Australians to borrow responsibly.(HT: The visible hand in economics)
In America, where populist post-Depression laws in many states have mandated loans be nonrecourse, the opposite is true. Americans can take out a mortgage more or less as a one-way bet. If you can't afford the repayments and can't refinance, you just send the keys back to the bank. Borrowers wipe their hands of liability. So, naturally, an American in financial strife will pay off debts that carry personal liability -- such as credit cards -- before they pay off their mortgage.
(Janet Albrechtsen in the WSJ)