The absence of income is not a "loss", certainly not a taxable one. This is not how landlords make money.
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.
An apartment with an assumed rental value of $X can sit empty and still be assumed to pull $X.
As soon as they start renting it out for $Y, the financials might have to be re-evaluated, which might prompt extra collateral from the borrower.
I have no idea how reliable this comment may have been, but it's an idea...