Sounds like the difference between GQ posters and Pit posters. 
I’ve been leaning this way. I don’t think it’s given that the differences in bone structure were readily apparent in a fully fleshed out face. If the larger bony projections aren’t visible they’re not going to be a factor in sexual selection. Any differences could as easily be explained as a less complex lower resource means of providing room for larger brains without making delivery of newborns more difficult.
Even if they weren’t correlated, the belief, even a subconscious association, would be enough to be a factor.
I also have a memory (can’t track down the source) that women in poorer countries tend to prefer men with rougher facial features.
As social organization among humans began to involve more and more individuals and small groups, and as human society grew increasingly specialized and complex, perhaps features which might be described as “softer” actually registered a wider and more precise array of facial expressions - these in themselves can be a profound form of communication.
Particularly among hunters: among a band of hunters, a gaze in one direction or another, a lift of the eyebrow, a quirk of the mouth can give silent directions about the location of quarry.
During battle, or when encountering potentially hostile bands: whom to trust? What might this stranger be up to? Is my underling truly loyal to me? Are my men really with me? Where is the enemy?
Among extended family members who live together: who are allies; who are on the outs. Who is currying favor with the patriarch; whose fond gaze does the matriarch’s eye fall upon? Everyone needs to know . . . and respond accordingly.
Facial expressions - much quicker than words - lightning fast; and much more difficult to prevaricate or fabricate with them. I’d say critical to a complex human civilization.
And a softer facial structure provides a more varied “canvas” upon which these many messages can appear, in all their subtleties of hue, saturation, light, shadow, and tone.
I have heard the opinion that women’s facial features are softer than those of men because a special role of women is often to form the primary bond with the newborn infant, and so the softness and delicacy of her mother’s features give reassurance to the infant of its mother’s love, assists the infant to recognize its mother’s face instantly, and helps the infant to develop the necessary neurological wiring with which to carry on social interactions, by practicing making these facial expressions with its mother, and responding to hers. Mother and baby thus become “one” as a social unit, instead of as a biological unit, as might be said to have been the case - figuratively - during gestation.
Perhaps also becoming “one” to one extent or another, with another human or humans is exactly what these social bonds are about, and doing so enhances the success of more complex and abstract communication involving bodily gestures and verbalizing.
Perhaps also, to the extent that eye movements, facial expressions, words, gestures, and tones of voice communicate the same message, humans feel they can trust the communication. And to the extent that any one of these modalities of communication is at variance with one or more of the others, humans sense that something about the other person may be “off.” Which can be a life or death thing to know about others.
All speculation on my part.
nm
One of the experiments they talk about in evolutionary bio textbooks is little vole creatures and their mating calls. To sum it up, it turns out that the voles prefer to hear mating calls that are more complex. Researchers found you can make artificially complex mating calls that no living vole ever emits and that the voles prefer the artificial call over a recording emitting by a real female.
Their conclusion was evolution is imperfect, it ‘designed’ through trial an error a neural subsystem in the vole. That neural subsystem ‘prefers’ things that don’t even exist, it’s buggy.
Similarly, in humans, we advertise and create dolls of women with proportions that almost no woman alive has. Legs so long and skinny they wouldn’t support any weight. Hips so narrow the woman wouldn’t be able to birth any offspring. Necks so long and slender they’d have neck pain for their entire life.
Obviously this isn’t evolution playing a deeper game, it’s just a buggy neural subsystem that only worked well enough to get to this point.