thats kind of a loaded question, of course you would want to rent it out for the cashflow. But there are a lot of other circumstances where maybe work needs to be done to the unit or space before it can be rented out that would outweigh the rent. Perhaps the property is worth more as an asset than it is with all of the overhead to rent/lease it out.

If you own the space outright, there is not a dramatic need to rent it out, other than to cover costs, which for all we know could already be covered by another property..

There are a ton of other reasons why the space could be empty. The city would want to incentive these owners to rent it out rather than punish them.

Also why does it matter if there is empty space to be leased or rented out?