It's because those rent prices are being used as collateral for other commercial real estate property loans. The rent price used is based on the rent the previous tenant paid, not the market value of the property.

If the owner leases at a lower rent price, they will essentially get margin called on their other properties. Therefore it actually might make sense to just have the property sit vacant with a (now) ridiculous rental price.

If governments start implementing a vacancy tax that grows as vacancy duration increases, essentially forcing the market to unstick, we'd likely see a rapid implosion of commercial real estate.