There's usually some excuse along the line of "Oh, the C-suite is constantly on the phone" / "Oh, the C-suite has to conduct business that cannot yet be shared

There's usually some excuse along the line of "Oh, the C-suite is constantly on the phone" / "Oh, the C-suite has to conduct business that cannot yet be shared with all the employees" / "Oh, the C-suite has to conduct private HR business" that makes it necessary for the C-suite to have a private office.