Why does it matter whether it's a resistance fighter or a soldier? And CoD3 having them is just more evidence that this is not a recent phenomenon.
Because female resistance fighters were more frequent than soldiers. And I don't think the actual inclusion of female characters is the issue here, but rather the occurence and frequency of including them as a token focus character in every game (or at least putting them in the spotlight like Battlefield).
I won't go out of the way to not buy the game for that - let the devs do what they want. It doesn't change my gameplay experience - but it does seem unnecessary. Especially since people on the other side of the spectrum complain if there isn't a certain type of people in a game (see Kingdom Come: Deliverance), even though the representation is strong in numerous other games.