I don't see any kind of mathematical gymnastics that has landlords making more money on vacancies.

Any tax they'd save would be a fraction what would otherwise be revenue. Besides, real-estate investors attempt to keep their costs (interest, depreciation, etc) all very close to their revenue, not the other way around. Less revenue is simply less of a chance to deduct expenses (not to mention less money for them).

The only way I think it makes sense is if they're sure they're going to be able to rent it for more if they hold out in a way that would make up for the short term loss.