With regard to a reversed image, you need to answer the question: "Reversed relative to what?" Imagine you're looking at a rear-view mirror in a car. The "reversal" is a reflection and refers to the image in the rear-view mirror being reversed relative to the image you would see if you turned around and looked directly out the back window. If this is so, then the answer depends on HOW you would turn around. Most likely you would rotate our field of view about a vertical axis, so the image you see will be reversed laterally (left-to-right). Of course, if you turn about a horizontal axis, the image you see would be reversed top-to-bottom.

This is an answer I was given many years ago by a physics teacher. You might as well ask why all points of an image aren't reflected at all points - a bit like a kaleidoscope...