Why Do They Always Make the Woman Hold the Derringer?

Megan Fox is going to be in a film called Jonah Hex
In this movie poster for the upcoming film Jonah Hex, you see the wonderful and talented Megan Fox. And, she's holding a derringer pistol.

Now, why on Earth would you make her hold the derringer? Why not give her a whip or a Gatling Gun? Why not give her a .44 magnum? I realize that there are plot considerations, story lines, and I also realize that Megan Fox is a small young woman with exceptionally delicate hands, but why isn't she walking around with a Springfield Rifle or numchucks? I don't care about your little comic book plots and your "true to the original" considerations. There is money on the line here. Know what money is, geek boy?

Haven't we evolved as a society since the olden days? Aren't we getting to the point where a woman can carry a pistol and not have it be a wimpy little derringer? Aren't there small men who could carry a derringer in a movie, freeing up Megan to wield a battle axe with a shotgun on the end of it and a chainsaw on the hilt that cuts off heads and shoots them down a long hallway?

Come on, Hollywood. Give the girl something better to hold. Besides, of course, my heart and my everlasting affection...

I'm sorry. I have to go weep now.