I gave you an example of my house, have not I? If I were interested in renting it I would not be "underwater" and any non-negative rent would be better for me than selling/renovating/keeping it off market. Note that I am not making a statement about every house, to rebut your assertion that all renters pay no less than the landlord's taxes + mortgage + insurance it's enough to show some (even one) counter example and not to prove that all or, even, typical renter does not do so. There are certainly rental properties that make profit on rent but I have few friends who rent their houses at less than their own expenses because they just cannot find tenants willing to pay more.

Seeing how in general rents had been lower than mortgage for quite a while it's sane to assume that I am not an owner of a unique house with a selected group of friends who are in this completely extreme situation.