Which is that it's keeping the space open for more productive use in the long term.
Suppose you own a storefront or apartment that could fetch $5K/month right now, but you think it will fetch $10K/month in 3 years, and that leases are 10 years long.
Well, the people/businesses who can afford $10K/month are by definition more economically productive: the people must have higher-paying jobs, and the businesses must be more productive economically.
If economic trends are such that you expect them to show up in 3 years ago but not right now, it's overall more productive for society to keep the properties empty for 3 years, and then get 7 years of the doubled rent.
Otherwise, if you were forced into 10-year leases now, then in 3 years' time, all those people and businesses won't have locations they can move into. Because of supply and demand, the small remaining inventory will be pushed up to, say, $20K/month, which will be unaffordable, and the city will be left with less economically productive people/business locked in, and economic growth will happen in other locations instead.
Now, certain laws/zoning/factors can distort this in possibly undesirable ways, and if you don't like gentrification then you won't like that either. And all this depends on where the market thinks the economy is going -- landlords are taking a bet, and there's no guarantee they'll be right, but that's the case with any investment.
But as a general rule, landlords letting properties sit vacant are actually providing an economic service, by ensuring future availability when it's even more valuable. Yet articles about vacant properties rarely seem to mention this. I'm not sure why.