There is analogy with open office. Only non-management unthinking drones sit in the open, all mgmt and all "thought workers" have offices with doors because we pay them to concentrate, you can't concentrate in a noisy environment, and if you don't have a door you can close you aren't suppose to be thinking, you're supposed to be laboring (even if the labor is paper shuffling or talking on a phone). Also a significant sign of social status, the idea that a member of management wouldn't have an office with a door is unthinkable. To be honest I think the only thing that has changed with the open office fad, is the unthinking drones are very aspirational and refuse to think of themselves the way management thinks of them.