Another really big issue, is that on tv females are by far the largest segment of the audience. In film its the reverse with Men driving ticket sales.
Hollywood is seriously scarred of medium to large scale budgets for a female action star.
In Alien, it was an assemble, and a horror piece. By the time Aliens came out, Fox had years to get information on the sales both at movies and home box office, and you can always argue that for many its the alien that the main draw.
With Sarah Conner, sorry the movie's draw was never Sarah. Really its the underworld, resident evil films that have a female driven lead, but those were originally fairly low cost films, that continued by aiming low.
Warners wants a hit, a large hit. That type of approach isn't going to produce a big hit, at best you get a district nine size success. And I really don't think the studio is willing to try for that.