Good point! Is the real estate they presently operate from not marketable for some reason?
It is likely not premium real estate. If you drive by it, the area is full of rather old and decrepit factory and warehouse buildings, many looking like they are not in use (which may be deceptive and a good mask for sweatshops inside!). I would guess that, today, the cost of doing engineering, getting new land and permits and moving would just not be worth it for an AM station.