Ah but long hair better shows health, youth and fertility; it is only feminine, if at all for that reason. Once again male hair length is irrelevant as a mate value factor.
In what way does long hair show youth and fertility? At best I could give you health, because it might give a bit more luster to the hair, which could be more easily seen the more hair you have, but there are better ways to judge health than the sheen of one's hair.
But youth and fertility? In what way does long hair show that a woman is fertile? And I have never heard of anyone who can guess the age of someone by looking at how long their hair is.
The social environment is a filter, nothing more. I think we shall have to agree to disagree. I believe biology to be a primary, exceeding cultural and social power and you appear to believe the opposite. We shall not make headway in this manner. And I honestly have no idea how you can make the statement that what was appealing in the 50's was vastly different from today. No clue.
As others have already said, it is a historical fact that beauty ideals have changed over time. There are some basic biological factors at play when choosing mates, but sociological factors are considerably more important.