[goda90]

The financial motivation is in keeping rents high. The units are empty because no more people want to pay as much as they are charging. Then it becomes a balancing act. An empty unit might cost you X, but to find a tenant for it might require you to lower rent by Y. If X * # of empty units is less than Y * # of occupied units, then it makes more sense to leave them empty.

[JoshTriplett]

As noted elsewhere in the thread, that simplified model assumes all the units must have the same price.

[Qwertious]

No it doesn't. It assumes some of the units have correlated prices, because units are, to some extent, fungible - if there are no one-bedroom apartments in the price range, then you'll drive up the price of pricier two-bedroom apartments due to the increased competition.

[richbell]

It isn't just a hypothetical. Landlords use companies like RealPage to collude on pricing and keep units vacant.

[JoshTriplett]

I wasn't suggesting that the net result was false, just that the model suggested in the comment I was replying to wasn't accurate, because landlords do sell the same model of apartment to different people at different prices based on when their lease started.