The plumbing systems in commercial buildings are not big enough to handle residents usage. Residents use more water and the outbound sewage systems need to be larger.
History favors the bold, and code inspectors blabbering about "written in blood" don't see all the homeless people they kill via reduced access to housing.
I've seen plenty of artist collectives that manage it; on paper they are office/industrial but actually everyone lives there. Every once in awhile one burns down but the mortality rate isn't as high as living on the streets which is ultimately what happens to those on the bottom of the socio-economic pyramid when the ones higher up push the ones under them down a rung to snag housing.
You also then had everything pretty much isolated to two rooms for an entire floor meanwhile now every unit is going to have a separate kitchen, a bathroom (or two, or three), a laundry room, etc.
And you're going to need a good bit of engineering studies done before you start cutting that many holes in the floor.
These seem like extremely solve-able problems.
Not saying it can't ever be done, it really depends on the building. But its not necessarily a good assumption it can be done well in a cost-effective fashion.
Demolishing the office building and building a residential building is more profitable often.
The economics just often work out a lot better to tear down the old structure and rebuild a new one more fit for purpose.
Sure, you could just cram the residences to the edges and try to recoup the cost of the rest of the square footage for places that don't need natural light. But once again you've got issues with original designs and intents for the building. None of the plumbing is designed to be pushed to the edges, so you'll need to make massive changes to the structural integrity by drilling a bunch of new floor cores to do all the new plumbing work. You could rent the interior spaces as storage, but you'll probably quickly flood the market of storage units with the massive amount of square footage you'll be bringing.
Trying to have industrial in there as well is asking for problems. Trying to rent some 15th story small/medium interior unit as some kind of industrial workshop would be quite weird. What kind of industry would want a smaller interior space that probably can't support heavy equipment, has a limit to ceilings of ~10 or so feet, can't require odd ventilation or strange/additional fire suppression/separation requirements, probably has significant power limitations (in terms of industrial capacity, at least), noise limitations, difficulty getting much product in and out, etc? Stuff that the city is going to be OK zoning literally across the hall from people trying to live? And that you're going to find a number of these willing to pay a good bit for such a space to cover the maintenance costs? These buildings weren't built for industrial usages, they were built for office desks and couches. Maybe a few floors have been upgraded to handle additional weight to have datacenter kind of spaces, but definitely not most of the floors.
So then you're trying to spread the maintenance costs of this massive and old building across higher value residences and a lot of very low value storage/weird industrial tenants.
You can Swiss-cheese a pan and deck concrete floor with core-drilled holes, the important thing is GPDR scanning before coring to avoid the pre- or post-tension cables embedded in the concrete.
I'm sure many many people have thought of all sort of solutions as the value for finding some sort of solution is extremely high.
A 20,000 sq ft office tower floor will usually have a single set of restrooms and a couple of kitchen sinks, maybe a dishwasher, plus a couple 6-gallon or instahot water heaters. If you subdivide that floor into a dozen units, that’s 12 showers, 12 washers, 12 dishwashers, 12 toilets, 24 sinks, and 12 water heaters.
The riser and drain pipes aren’t big enough to handle residential needs.
They might subdivide it 12 ways, but there is one shared kitchen for a whole floor and maybe 2 toilets, 2 sinks and the residents are going to the laundromats. They tend to put the shared amenities on the ground floor as much as possible because it is easiest to expand them there. It beats being homeless by a long shot.
For reference, when I hauled water, we used about 60 gallons a week for a family, or about 0.05% utilization of a 3" drain pipe for a single family. You do not need much water in order to be way way better off than being homeless; 5/gal a day of non-potable water and you're pretty much in luxury comparatively and a shit-ton of people can be putting that down a 3" or even 2" drain pipe before it causes problems. A 3" pipe is the minimum that would be serving a typical floor of a warehouse, so plenty enough for a constantly used couple of shared bathrooms with a shared kitchen. Honestly even splitting it 12 ways could be overcome with some technical ingenuity (electric lock-outs to prevent more than a few in use at once, and AAVs to prevent needing a bunch of new vents).
These are all easily overcome problems for people utilizing an ounce of civil disobedience with regards to the code. And yes I have personally done all the design and plumbing and electric for multi-structure properties (though not the black market ones).
It didn’t work out so great in Oakland at the Ghost Ship, 36 people died in a similar arrangement.
Building code is written in blood, things are done a certain way for a reason. You may be morally or ethically against them but following code saves lives.
Not having housing didn't work out great for 700+ dead homeless people per year that are estimated to die of hypothermia.
The code inspectors have blood in their hands. You may be morally or ethically against bypassing the codes, but bypassing it can save lives.
Black market housing is done for a reason, a very good one, and one that saves lives. Fortunately where I live, I built a house without any inspections whatsoever, so none of the code psychopaths were even around to make their absurd case about the ghost ship, and that is the only reason why I was even able to afford to own a house.