Angular resolution, not "screen real estate". It limits information density. Yes, the VR headsets have much higher FoV than a monitor, but it hardly matters for desktop work. Angular resolution is much higher on a monitor. Swiveling your head constantly to look at low-res windows floating all around absolutely sucks compared to having one monitor in front of you with higher information density. Varjo is the exception, and yes I'd say Varjo's resolution is good enough, but Vision Pro is borderline and Quest/Frame are much worse.