Why do people wear their watches facedown from their wrist?

Thinner people or people with large or protruding wrist bones find it much more comfortable to wear a wrist watch face down so that the largest part of the watch (the face) is not bruising and scraping their wrist bones all day.

That's how they wear it in the army, so men can check the time while holding their rifle. I think that is why it is fashionable.