Well it is, at its simplest, a marketing strategy. 

Video games are stereotypically "a guy thing", and what tends to get guys' attention? Attractive women. 

And whether it's a matter of these marketing techniques actually working or just the fact that they're impossible to avoid now, these games sell. And that encourages game developers to keep going with it. 

So really I think the biggest thing that would need to change is for the game industry to acknowledge that there are more female gamers out there than they think. The only games I ever really see marketed towards females are kids' games, so the "hardcore" gamers are still primarily male, in the eyes of the developers. Bringing more female gamers of that age to their attention might make them change their portrayal of women a little.