As artist, you would want to draw persons facing towards viewer. It makes pictures usually more compelling. When drawing correctly, you would efficiently cover half the body or rotate the person away from the viewer.
Running is awkward pose, as half the body seems to be rotated the other way always. But in a art, it is preferable to have subject moving one certain way.
So it is only natural to pose people like this, if you are uncertain how they are in real life or it does not matter. Because it is way more aesthetically and understandable for the viewer. In creek example, you could show persons genitals and upper muscular body, not only one of them.