But you don't rent by cubicle, you rent by floor or building. So adding a new employee when you have hit your max means you have to figure something out or sink a whole lot of money into a new building for one person.
Office in NYC was remodeled to open office, and the limits were determined by fire code, bathrooms, etc. In the end, a whole bunch of valuable floor space is sitting empty as relaxation rooms, a puzzle table, and funky couch areas that nobody wants to sit at because it’s next to a big boss’s office.
Practically speaking, most people are treating the shift as an implicit agreement that employees can work from home 90+% of the time.