If star power was the be-all end-all, then half of the Avengers wouldn't have gotten their own movies.All that, and ScarJo is a known quantity WITH star power. It's proven she can play the action role of a tough lady who can beat up anyone you can name, and tacking her name on the movie draws in more people than a little known or unknown actress who only gets the part because the source material comes from japan, despite it not looking japanese at all.
And you know how you make actresses known? Get them in movies.