I can give a possible answer, but it's based on optics rather than history or aesthetics. Your mental image of a person is based on the view from about 15' / 5m away. If a front-on photograph is taken from closer than that, there is a distortion of the face. The camera can't see part of the side of the face, and the centre of the face moves outwards on the image towards the edge of the face. This is not a lens distortion, it's just caused by where you are standing. You can try this yourself. It's also the reason why photobooths give rather odd looks.

The way a photographer deals with this in modern times is to stand at least 5m back from the subject, and use different focal lengths to capture full body, top half, head and shoulders or head only. However early photographers would not have a wide choice of lens and might only have one. This would probably be a "normal" lens, i.e. one which would give roughly the same angle of view as the human eye. This would be fine for a full-length portrait, but too short a focal length for a head and shoulders shot.

Given this limitation, the photographer would have to get much closer, running in to the distortion problem. However this can be avoided by using a side-on shot. The same optical effect applies, but because there is little or no "side" to the nose in this position, and the back of the head is ill-defined, the face looks much less distorted. This can be used on modern wide-angle fixed lens cameras as well - here I mean mobile phone cameras.

A further possibility is depth of field. Due to the large plate or film in use (at least 4x5", perhaps 8x10"), depth of field is narrow compared with modern cameras. You can see this if you look at the right shoulder in the Woolf photo. A side shot puts the nose, nearer eye and the mouth at roughly the same range from the camera, making it easier to keep them all in focus.

Having said all that, they could be side on purely for aesthetics. The photo of Woolf in particular is beautiful, and would lose most of its effect if taken face on.