The same principle explains why many rust belt cities have vast areas of abandoned tracts. It's not that they actually lost people. Regionally speaking, most of them didn't. But sprawl created new homes while not adding new families to live in the old ones. The math in both cases is pretty straightforward.

>> (the pigeon hole principle, actually).

IE if there are 10 houses for rent and 11 people want to rent, there will be one house in which will have two people trying to rent it.. lol