I remember clearly being taught, but I'm not absolutely sure if it was from monks at the temple or in reading, that the hair was/is looked at as what gives us beauty and makes us attractive, and also makes us vain and conceited about our looks. In shaving our heads and bodies we are cutting off our attachements to vanity, and giving up much of our beauty to be humble, and one thing I'm thinking but don't remember being taught, there is that certain sameness about all monks and nuns having no hair, that builds a kind of camaraderie among the monks in that they all look similar. Imagine all the competition that would be involved in different monks haircuts if they didn't shave their heads, one monk would get jealous about another monk haveing better or longer hair, etc etc etc
So a lot to establish a sense of sameness between all the monks, and to establish an obvious differentness from the laypeople
Last I might postulate a shaved head doesn't look pretentious like a fancy haircut, shaved looks down to earth, humble simple.
18 years ago I made one of the most important decisions of my life and entered a local Cambodian Buddhist Temple as a temple boy and, for only 3 weeks, an actual Therevada Buddhist monk. I am not a scholar, great meditator, or authority on Buddhism, but Buddhism is something I love from the Bottom of my heart. It has taught me sobriety, morality, peace, and very importantly that my suffering is optional, and doesn't have to run my life. I hope to give back what little I can to the Buddhist community, sincerely former monk Johnhttp://trickleupeconomictheory.blogspot.com/