Men are practical animals. From the time of Sparta, Spartans and Greek soldiers kept their hair short for practicality in battle. The Romans adopted short hair as a symbol of discipline, hygiene, and civilization, especially during the Republic and early Empire. Later on, the French military under Napoleon, adopted short hair for practical reasons as well. Roman military culture, and French military culture heavily influenced civilian fashion, making short hair the dominant style.
This is why society views long hair as feminine and short hair as masculine. It is also why you will see nearly all butch-bull dykes have short hair. They desperately want to look and act more "manly".