I said it's probably not the vocalist indeed who names themselves like that.
Yes, there are fewer females in metal. That's not a reason to keep using this term, you can actually also just be cool about it... Have you ever heard of people using the term "mexican fronted metal bands"? My favorite band in that "genre" is Slayer. There are fewer mexicans in the metal community and the vocals are impressive as well.
What about gay fronted metal bands? Nigger fronted metal bands? Or what about left handed fronted metal bands?
And once again, it's not the decision of the vocalist probably. It's the label and fans more likely.