We find long, thick, flowing hair attractive because it is a sign of health and youth, therefore a sign that she is a good partner to have children with. The hair gets more brittle with old age or from disease.
It is the same as why we find smooth skin with a healthy pallor attractive, a straight back, a small nose and chin and ears (these never stop growing, so they are bigger in old age), wide cheekbones (make the face look less drawn-out; the face grows longer with old age), large eyes (eyes are larger in proportion to the face when we are children), white teeth, a clear voice, a healthy breath, etc. We also find a certain symmetry in the face attractive, called the "beauty mask", as that symmetry signals health - those who deviate a lot from this symmetry usually have poorer genes. In women, we appreciate a certain hip-to-waist ratio as it signals good child-rearing capacity, and we find slim shoulders attractive in women as that signals more estrogen, less testosterone, therefore a better mate to have children with.
And so on. Evolutionary psychology should be taught in school. Of course, since the extreme-egalitarian doctrine demands that we pretend all traits are equally attractive so that no one is sad, this wisdom will never be told to school children. Except by an old teacher I had who couldn't care less about what the school system said, and taught us whatever he knew to be true. I liked that man. Note that I don't say "guy". Some men are not guys or buddies or bros but men, period.
