I don't think you can reduce it to one factor. A lot of people bought into the idea they could create a new Bell Labs for their advertising/CRUD app/whatever by using open offices. And as many others have mentioned it was cheaper. I don't think your argument is wrong but it comes across a bit myopic.
like a lot of people buy into the idea that unlimited vacation is actually unlimited? Only the truly naive would believe that company BS. Don't get started on company "culture".
