Ouch, I didn't know that. I didn't know why there's no actress in kabuki. I'd never doubted why until I read this book (A Short History of Asia by Colin Mason). Well, as the title of the book shows, it's really a concise description of Asian history, and therefore, reference to kabuki is also short. Actually, it's just a sentence. But the one sentence explained why.
Because its productions were so often ribald and erotic the (Tokugawa) bakufu forbade the employment of actresses in kabuki, so female roles had to be taken by men. (Mason, 2005:102)
Damn it, I'm not qualified to be a Japanese :(