The rear stairs are normally used by service personnel, cleaning crews, etc. It might not be a common practice *everywhere*, that's why some user assume the stairs shouldn't be there.
We made them appear as the default option, because some airplanes, including all the default ones, might not have a separate control for the rear passenger door, which is opened together with the front doors so, if we didn't had the rear stairs, it would look strange having a door opened with no stairs attached.
Of course, like anything else in GSX, this can be customized, using the "Disable Staircases" option in the parking customization page which, as all the other settings in that page, can be set for a single parking, a group of selected parkings, a whole terminal, or the whole airport at once, depending what you selected in the left hand tree structure.
