I don't think it's biological. I think maybe the industry was just bigger for males.

Take Tara Strong. Sure, lots of her voices sound a little similar (you might hear Timmy Turner, then hear the girl in Batman, and think "oh yeah, they do sound similar" once you knew they were the same voice). But she can definitely "transform" her voice.

The male voice actors on The Simpsons have incredibly transformative voices, which I think comes from lots of practice in the industry. The first time I saw a chart of all the voices for each character they play, I couldn't believe it. After paying very VERY close attention, I can kind of hear Mr. Burns in Moe, but just barely.