There are sometimes some strange issues with office construction.
There might be no plumbing in the locations people will want for toilets and baths and kitchens in the individual suites away from the core of the building. Same goes for retrofitted laundry facilities.
HVAC systems (in the US anyways) are often centrallized and might need a lot of retrofitting to make it work like a condo/apartment.
Kitchen ventilation
Windows might not open, can't get to a fresh air source
Aside from that stuff, the issue of empty office buildings while we are experiencing unsustainable housing markets is begging for a solution to address the demand.
There will probably be a handy sum to be earned for construction companies who get efficient at conversions.
It's not that there might not be plumbing, it's that there is zero plumbing in most office buildings aside from one clustered section for floor where there's 5 to 10 toilets for each gender.
On top of that, you have completely different mechanical systems. An office building for instance may have one single mechanical system for the entire building, whereas an apartment would need separate mechanical systems for each individual apartment.
Then you have the kitchens, bedrooms and interior partition walls that are vastly different than an office building, plus the requirements for exterior windows which precludes larger office buildings with deeper floor plates from being converted at all without demolishing the interior portion of the building. Curtain wall systems that may or may not be compatible between an office and residential building (non-operating windows)... Not to mention the stair and elevator systems are probably not going to work either.
So in the end you're probably looking at gutting the building down to the structure and removing every piece of the building including the outer envelope, roof, all of the electrical plumbing and mechanical systems... In the end it may or may not be cheaper just to build a new building from the ground up.
Source: am architect. And yes, I have done conversions like this in the past.
I wonder if it would be possible to require all future construction to be designed in a way that it could easily be switched between commercial/residential. Like each floor of an office building has to have plumbing roughed it to support x number of toilets/showers on each floor, stuff like that.
Also offices don't require that all the rooms have access to natural light the way residential buildings do. That's why office towers can be thicc blocks while apartment buildings often need to be U-shaped.