I loathe full height single person cubes personally, however it was explained to me at my current job (large multinational) that one rationale for cube farms is that legal can treat these as 'laboratory conditions'. It's common for us to work with prototype hardware which might involve legal agreements, but from a practical level I find this rather pathetic.
There's also the fact that in many jurisdictions, things like cube walls can be depreciated like office furniture, whereas building actual walls counts as an improvement on the building - making the cubes even cheaper/more tax-efficient.
