The answer is pretty simple. When capturing the beauty of a model, a headshot forces you to leave out 90% of that beauty - and that is what I call a crying shame! It feels so restrictive. Here is the result from a vision I had, employing a purplish satin background, featuring my friend Anne:
One the other hand, it does make the viewer wonder what the other 90% of the model looks like! In addition, the headshot poses a creative challenge for both the photographer and model - similar to asking an artist to paint a masterpiece using only 10% of his or her paint colors.