It’s no secret that men are more sexually attracted to women then vice versa. I’ve never heard of a woman who was distracted by a male rabbi’s sermon due to his being good-looking. And any man who says that he wouldn’t be distracted by a female rabbi is probably in denial, or has become overwhelmingly desensitized to female sexuality, probably due to overexposure. That desensitization is precisely what Orthodox Judaism tries to avoid: we want husbands and wives to have passionate, romantic relationships with each other instead of lukewarm marriages in which the power of physicality has been diluted. Having more female rabbis might accustom men to being less distracted, but that’s an inherent negative because Judaism sees desensitization as a lose-lose.
Rachel Wizenfeld, “Why I’m OK Staying Out of The ‘Orthodox Boys’ Club'”, The Sisterhood (21 August 2015) [http://forward.com/sisterhood/319559/why-im-ok-staying-out-of-the-orthodox-boys-club/]