Why do hotels put mirrors?

Because you are staying in an old hotel, or a hotel designed by a non-professional, or the room layout cannot be changed;

Because of the layout of the hotel room, the opposite side of the bed is the writing desk (which is not easy to place in other places), and the toilet mirror is on the writing desk;

Now many hotels have cancelled this design (there are indeed unreasonable reasons you said), and designed dressing tables in other places, adding makeup magnifying glasses and other functions. In this way, there are only TVs, decorative paintings and artworks hanging on the wall opposite the bed.