I don't really buy it but a potential reason is that people above a certain level have a business need for a private space. Say you need to be on the phone all

I don't really buy it but a potential reason is that people above a certain level have a business need for a private space. Say you need to be on the phone all day talking about privileged information like the upcoming earnings call or a major business deal. Even at lower levels than that, maybe someone wants to come to you in private with a complaint or maybe you need to tell someone they're underperforming. You could do these things in meeting rooms like everyone else but if you're doing it 75% of the time you're working, you may as well have a private meeting room (i.e. office). There's also security. People with higher privileges have more sensitive information that needs to be better protected. Yes workstations should be encrypted and confidential paper documents shouldn't be laying around the office but defence in depth is a thing. Efficiency is another concern. The time of people at a certain level is extremely valuable and it can be wasted on suboptimal collaboration. Their time needs to be planned very carefully. And finally, it's just a perk.