So you, the property owner, end up in a situation where if you lower rent to attract a new tenant, the bank will recalculate your loan, potentially ending in a margin call.
Because you are a heavily leveraged house of cards, a rug pull on a few of these loans could cause a cascade liquidating your commercial inventory. Your business is buy a property, take a loan against it, use that loan to buy a property, etc etc.
Therefore it becomes worth it to carry vacant properties, because they are acting as the stilts holding up your money making properties. The vacancy becomes a cost of doing business, and gets factored into the rent of places that are getting leased.
The current location my office is in, was vacant for 12 years before we signed a lease, owned by a big name commercial real estate firm.