Because there are a thousand male leads out there, and variety is nice?
They've never written one before, it could shake things up a bit. Stretch them as writers.
But WHY isn't it fit for it?
I honestly don't see any reason that a female character wouldn't work.
Saying its a 'testosterone game' doesn't really mean anything at all.
"We didn't really think about it this time"
That, right there, is the problem. It didn't even occur to them. There is no good reason that one of those characters couldn't be made into a woman with pretty much no change to the story.
But they didn't.
Cos they just 'didn't really think about it'. And never will.
I have to say, I strongly disagree with the authors view that "games should not be based on story, this isn't a movie or TV show".
No, games should be based on story. It is the central component which ties it all together. Without story, gameplay is just mathematics in a convoluted form.
Ok, yeah, that is a remarkably beautiful-looking game.