Why did Rodrigo Santoro play Xerxes?

Specifically, why did he play a giant, bald, androgynous Xerxes?

Let's review what we have:

1. Rodrigo Santoro is gorgeous.
2. Rodrigo Santoro possibly cannot act.
3. Xerxes, according to various crazy people, is huge, hairless, and epicene.
4. Rodrigo Santoro, notably, has great hair.
5. Rodrigo Santoro is cast in a part in which he is deranged and looks nothing like himself.

Do you see where this loses me?

People: there are ugly men and women out there who can act. You cannot pretend that they are beautiful, but they might be excellent for the part. Why do you go to the trouble to make beautiful people up for ugly rôles?

Same goes for Eric Bana in Star Trek. Thanks for nothing.