Whoa with the generalizations there, Worried19. Many boys & men in many cultures over history have worn long hair & wigs. Sometimes the styling has been casual & no-nonsense, in other cases the styling has been elaborate. Check out some paintings of Louis XIV.

Also, historically in the West, people in many countries hardly ever bathed - & rarely washed their hair. For example, in the 17th & 18th centuries when both wealthy women & men in France, England & other parts of of Europe wore elaborate hairstyles & wigs, hair was kept clean by use of powdering. There were even special rooms for powdering hair - which is where the term "powder room" still in use today comes from.

https://www.geriwalton.com/hair-powder-history-of-its-popularity-and-unpopularity/#:~:text=Hair%20powder%20was%20at%20one,were%20known%20to%20use%20flour.

Further, even in the eras and cultures where males customarily wear their hair short, it's not true that

The only thing most men are expected to do to their hair is wash it and comb it.

You might want to look into the history of hair pomades and products like Brylcreem. Also: https://youtu.be/nUb6-jtkLD4

And the vast majority of girls are trained from birth to keep their hair long. You don't ever see little girls with buzz cuts or close cropped heads. Even pixie cuts are very rare. Girls are trained to value long hair, and most parents keep their daughters' hair long.

Please specify what era, country & specific cultural milieu you are referring to. Your generalizations do not apply across all cultures & eras, nor do they apply to the "lived experience" of many of us from Western countries like the UK & UK who are living now. When I grew up in the NY metro area of US in the 1960s, pixie cuts were far more common than long hair in little girls, particularly girls from larger families. Most of the girls I knew were only allowed to grow our hair long when we became old enough to care for it ourselves. Our parents couldn't be bothered. And none of our mothers had long hair. This was true of both white & black people I knew.

I know many parents of many different generations who did & do not keep their daughters hair long & who certainly did not train girls "to value long hair." As a parent myself, I've never heard of that this is part of standard parenting dogma. Can you cite some of the parenting books that say this?

Finally, I must take issue with your claim that

the vast majority of girls are trained from birth to keep their hair long.

Have you ever seen any babies? Most of them are born nearly bald. If they have hair, it's patchy, fine & very short. The only way girls could be trained from birth to keep their hair long would be to give nenoates hair extensions.