This. I’ve worked in construction and it comes down to the fact none of the office building structures have the required egress clearances for emergency exits, they don’t have proper heating, plumbing, or electrical equipment to serve the demands of residential needs. They often don’t have the required window and lighting access, and even if you just took the floor plan “as-built” the layouts would be wonky at best. It’s an impossible solution, frankly. You’re better off converting a factory wearhouse to apartments. Office buildings make awful residential spaces, not inherently on purpose we have just shaved down to the bare minimum in terms of occupational requirements which fall well, well below the demands of residential requirements.