>>283453771
Downstream from what gives them inherent value (a womb), a woman's looks are the second most defining element of her existence to society and to the world around them. Hair is a very significant aspect of one's overall looks as, among other things, it frames the face and can dramatically alter how attractive people perceive you to be. For women, and many men, hair is equivalent to their identity. The trauma can come/comes from having that identity taken from them.
A hypothethical equivalent for men, whose value is largely determined by their body/their bodily efforts, and the resources that naturally result from that, would be something along the lines of building up your finances for 15 years and then one day being forced to give almost all of it away (or willingly giving it away to charity or what-have-you). Yes, you can rebuild your wealth, yes, you may not be completely destitute, but in the instant that your money/value is gone, your place in society is drastically altered. Granted, that's a slightly watered down version since for men, value to society and self-identity are not nearly as intimately tied as for women. For a truly traumatic equivalent, think of it as losing one of your arms or your legs. A lot of the masculine identity is tied up in being able to move through and have an impact on the world around you, in your agency, but then to suddenly be deprived of a large part of what gives you the ability to do so would be deeply traumatic to a lot of men.
tl;dr Hair = identity. Altering it is psychological, more-so if it's altered against your will. Men are not dissimilar, just look at all the online communities made up of bald/balding men.