Why does nature teach that long hair on a man is a shame?

Nature teaches that long hair on a man is a shame because it goes back to the custom of Rome, where men wore short cropped hair. This cultural norm, reflected in creation order, made long hair on a man appear shameful.

Les explains that Paul's point about nature teaching long hair on a man as a shame goes back to the custom of Rome, where men of those days wore rather short cropped hair. In contrast, a woman's long hair is a glory to her, for her hair is given her for a covering. Paul tempers his correction, not wanting the Corinthians to feel browbeaten or to rebel, yet insisting everything in the local church be done in order, for God is a God of order.

1 Corinthians 11:14

Doth not even nature itself teach you, that, if a man have long hair, it is a shame unto him?

Why does Paul say nature teaches that long hair is a shame to a man?

Paul appeals to nature and the likely Roman custom of short cropped hair for men to argue that long hair on a man is a shame. He contrasts this with a woman's long hair, which is her glory and given as a covering.