I personally know a landlord who will almost never rent out the commercial space in their property. Right now not renting it out saves then tax due to the “loss” they declare. But the price at which they’d have to rent the commercial unit to exceed that tax benefit would be high enough to cause a reappraisal of the entire building which would increase the property tax for all the residential units they pay as well, which would mean they’re losing money, or at least making less money, on each unit until they can increase the rent to level which may not be sustained by the market.
Another well known non government reason to leave units vacant is if the market value has dropped, leading it out at the lower market value can trigger all sorts of problems for the property owner with the banks who have lent money to them for the property, including the ability for them to recall the money early, change rates, etc since it may trigger clauses regd the appraised value dropping below a certain threshold. These are purely private contracts that provide a very strong incentive for landlords to keep spaces empty rather than lease them out at market value. This tends to be the most common reason for us city storefronts being empty.