I suspect that, in many cases, the homes were underwater and the banks made a calculated decision that it was better to have a delinquent borrower at least paying upkeep on the property.
Banks, just like borrowers, will sometimes choose to just walk away from underwater properties. There are whole neighborhoods in the Mon Valley like this. Detroit is actually paying to demolish these type of homes.
If you live in an area where homes sell with relative ease, it would not be wise to try this. The lender will foreclose on you just as soon as they are able to do so and the home will belong to someone else within a matter of weeks, tops.
There are at least 5 properties like this within a 2 block radius of my house they are semi foreclosed for 5-6 years now. None are for sale and according to a foreclosure investor there is two reasons for such, one the Bank doesn’t want to take the ‘hit’ and two they haven’t been able to untangle the note to a point where they know for sure who holds it. Those are the worse as the management companies stopped taking care of the place because no one is paying their fee so the house sits and deteriorates and becomes not only a eye sore, but worth less and less as time passes.