It’s amazing how much cheaper a fire is if it can be called in and put out before the entire building is engulfed. Plus, some people will break into anywhere.
Yes, a 24-inch CRT monitor was EXPENSIVE once upon a time. Today, 32-inch flat colour video screens are dirt cheap, and in all the heist movies security have a wall of 10 or 20. Also, many security systems will have a monitor at the reception desk where the security control computer cycles through a predetermined list. (One place I worked with made sure the camera looking down on the cash register was not on the rotation so the cashiers could not be certain what was or was not visible.)
Another factor is that now anyplace (or most places) worth monitoring and guarding also uses motion detectors and tracking software so that cameras pointed to closed doors don’t need to be shown until someone is approaching the door.
Yes, some of those programs that cycle the monitor vew through assorted cameras, also have an option to switch to the view to the camera where motion is detected. (in a priority order if multiple triggers happen)