Here's a thought

The Greeks always depicted their soldiers garbed in nothing but bronze helmets fighting an ostentatious and over-clothed Persian army. The Trojans were portrayed in this manner too.

Of course in actuality, the Greeks were more strongly armed than their counterparts, clad in heavy bronze versus the wicker and leather of their Persian opponents.

If you look at this way, then you could argue that Miller's 300 is actually tongue in cheek to how the Greeks viewed themselves. A contemporary reductio ad absurdum of the Greek vantage!

Though the more likely explanation is that Frank Miller is a bigot and fetishist for overly masculine men.

Next time: Through deconstructionism, I establish that King Leonidas and his escorts are in fact flaming homosexuals.