A tax write off is going to be worth, at best, ~35% of the value gained from actually leasing the property. That makes it considerably worse to hold on to.

Its far more complicated than that. Most of the owners of these properties are institutional, not individuals or small groups. They are far more concerned about the valuation of the real estate than it's cash flow. The cashflow side has issues too, but from a valuation perspective, once you sign a rent at a lower rate, then that will trigger a shift from the inflated, unrealized rent in the valuation model, to the actual rent in the lease. It's entirely likely that the dip in value from the signed lease is more impactful than the actual cashflow from that lease. It doesn't matter that you couldn't get the rent in the model today, since pushing out the assumption results in less of a hit in value than signing an actual lease would. This all gets billed as "the market will bounce back".

Remember there are a lot of upfront costs for the land lord as well. They put in a lot of money upfront for buildouts/base building work, and it may be 2-3 years before they actually break even on the money they put into the space. If you're not sure that the business model is going to last that long then it absolutely makes sense to sit on the vacancy.

Source: worked at a nationally invested REIT that had a good number of properties that have this same issue.

Waiting is a risk that may pay off, so that 35% write off still changes the math.

Suppose you are going to make a coin flip bet. On heads you win 1$ cents tails you win 0$. That's worth ~50 cents. Now, suddenly on tails you get 35 cents. By reducing the downside risk it's more worth it to make the bet (67.5 cents).

Tenants are a pain in the ass. Buildout (for which tenants often expect you to pay) is expensive. Unless you're leveraged to the hilt, you can afford a few quarters of loan payments on an already-built building. That being the case, signing up a marginal tenant is throwing good money after bad.

If the market has changed in permanent ways, and you're never going to see another good tenant, you want to learn that as soon as you can, and then get out. This is why our great leader always structured his deals so the company could declare bankruptcy and he could skate away with the previous profits.

This may be it. Lets take away this write-off option.