Cities with empty office buildings and severe housing shortages rarely convert one into the other at scale. The obstacles are physical properties of the buildings themselves.
Office floors are too deep
An office floorplate is designed to be wide, because open working space can sit far from a window and still function perfectly well under artificial light.
Homes cannot work that way, since bedrooms and living rooms need daylight and openable windows, and building rules in most places require them.
On a deep floor, that leaves a band of habitable space around the perimeter and a large windowless core in the middle that no residential layout can usefully absorb.
Plumbing has to go somewhere
An office building concentrates its water and waste in a small number of shared core locations, because a whole floor may be served by two sets of lavatories.
A residential floor needs a kitchen and a bathroom in every flat, and each of those needs a drainage route falling to a vertical stack.
Cutting new stacks means putting holes through every structural floor slab in the building, which is expensive, slow, and sometimes not permitted by the structure at all.
The facade is usually wrong
Many office buildings have sealed glazing, because the ventilation is mechanical and the windows were never intended to open.
Replacing a facade to provide openable windows and to meet residential insulation standards is one of the largest costs in a conversion, and it changes the building's appearance entirely.
Floor-to-ceiling glass also creates overheating in a home in a way it does not in an air-conditioned office occupied only during working hours.
Regulation applies differently to dwellings
Homes are held to stricter standards than workplaces for sound transmission between units, fire compartmentation and means of escape, because people sleep in them.
Retrofitting compartmentation into a structure designed as continuous open space means new walls, new protected corridors and often a second staircase.
Minimum room sizes, daylight requirements and parking rules vary widely between jurisdictions and change over time, and they frequently decide whether a scheme is viable at all.
The arithmetic often fails before it starts
An owner comparing conversion against holding the building empty is weighing a very large capital cost against an uncertain residential value in that location.
Offices in business districts sit where people work rather than where they want to live, and the surrounding amenities take years to follow.
Conversions that do proceed tend to be older, narrower buildings with modest floorplates, which is precisely the stock that is least likely to be sitting empty.