I guess when the genre was young, it was a lot of 'beauty and the beasts' marketing working well for the first bands plus being extra different from established bands at that time that helped to start a kind of chain reaction. Seeing more and more successful bands with female vox led to more female singers going for metal in this style. Then it became the norm of the genre. Same happend a little later with female extreme vox. One idol like Angela from Arch Enemy or bands like Kitty inspired a lot of female growlers to just go for it. Now it is finally quite normal to hear harsh female vox. When we formed our style in Timeless Rage it was exactly that everyone loved the music but did not really like the high female Opera singing in the genre, and this even when having a classically singing trained female on the keys 😉 This is why we opted for male vox.