In a masculism society, men are having absolute power, an ideal man in this society is described as strong, muscular, tall, wealthy, egocentric and power...etc.... while women are in a recessive position, they represent weak, soft, emotional, caretaking and passive. Therefore, not just the video games, but in our culture, like movies, TVs, magazines, advertisements... all images shown are in the idealism of what a gender should be.
Moreover, the society is changing in the recent years, feminism raised drastically, and people started to concern about the rights of the women more, so woman images change as the culture change. Woman could be strong, wealthy and having powers, as in the video games, female protagonist and heroine become necessary. They are no longer weak and can wield guns and fight as what a hero did.
Because men are visual creatures. Everyone love to see beautiful things, especially male. Therefore, to boost sales, making a attractive female character is probably one of the way to achieve this.
Who would wear this sexy outfit in a real fight? Is this possible to beat a enemy with such a skinny body? lol
{ I'm a feminist }