"Star Trek" is a commercial enterprise that must appeal to a wide audience to stay viable. To that end, it's always seemed to play it safe. And, if you're trying to get as many men aged 19 to 35 (or whatever) to watch your show on TV, the "playing it safe" means strong male characters, mini-skirts, and William Theiss costumes. Mostly male casts (at least as main characters) are an unfortunate part of Hollywood on the big screen and on TV. Look at the broo-hah-hah that was created about women being cast in the lead roles in the new "Ghostbusters".
I'd say part of the problem with the reboot of "Star Trek" in 2009 was it was so faithful to TOS, it took some of its negative baggage: Kirk the womanizer, mostly male main characters, and mini-skirts with it. On the fringes, where it could play with the characters, it's tried to put women in important roles. Carol Marcus is a strong character in TWOK. Uhura is finally given something important to do in TSFS. There's a woman starship captain in TVH and Gillian is a strong character who is not played as just a romantic foil for Kirk. Saavik, Valeris, Martia, Azetbur, the Borg queen, Commodore Paris, Jaylah, and a few others have been strong female Trek characters (that could've been cast as men without changing the stories a lot). But when you start with six of the original big seven being men, it's going to be hard to get real equality of number.
I'd say part of the problem with the reboot of "Star Trek" in 2009 was it was so faithful to TOS, it took some of its negative baggage: Kirk the womanizer, mostly male main characters, and mini-skirts with it. On the fringes, where it could play with the characters, it's tried to put women in important roles. Carol Marcus is a strong character in TWOK. Uhura is finally given something important to do in TSFS. There's a woman starship captain in TVH and Gillian is a strong character who is not played as just a romantic foil for Kirk. Saavik, Valeris, Martia, Azetbur, the Borg queen, Commodore Paris, Jaylah, and a few others have been strong female Trek characters (that could've been cast as men without changing the stories a lot). But when you start with six of the original big seven being men, it's going to be hard to get real equality of number.