I don't think they want to pay it....they stopped making payments at the exact time Nadya became pregnant with the octos so I'm sure they assumed they would be given a new one or given enough money to buy one. The house they are in is obviously trashed....so they are better off to just let it go to repo than to pay it off and try to sell a broken down, filthy house.
Great insight! (The photos of the home look like no one has even bothered unpacking or making it home-like.) I don't think anyone really believed that they'd have to wait this long for their big payday... JMO.