The main way if you look at it is investors willing to run on empty - buying houses and then failing to rent them at the amounts they're trying to get, where they sit empty for some time before the investor goes belly up.
So in this case the investor is taking a few hundred thousand dollar loss so the building can then be sold for a loss and rented at a price that makes market rent make sense?
I feel restrictive zoning is a much bigger issue than empty unsustainable houses.
