The arguments against conversion assume you care about the current owner's financial situation.
You'd also have to install a bunch of showers, which could be a significant problem on its own.
And then there's the increased amount of sewage, which the building might not be able to handle - even the local sewers might not be equipped to handle the uh... Load a large commercial building would generate with 24/7 occupancy vs 8/5 occupancy.
The reason you don't see folks converting commercial spaces into residential isn't because it's not wildly profitable, but because building new purpose-built residential buildings would be cheaper than a conversion for anything other than one or two floors.
They have been going wild in the UK converting office space to residential.
I do see this. That's my point. Your plumbing problem has been solved by not jamming a ton of people into the building.
How is there more than an office full of people?
Compared to installing a new domestic water pipe riser and drains in an office tower (plus pumps, pressure tanks, etc), installing a shower in each unit is essentially free.
Connect the in-unit supply lines to the tap, core drill a hole in the floor to get to the floor below and connect to the drain piping, done.