I'm not going to say that they don't have good credits. The Russo brothers have been with the TV show Community as directors and executive producers since its inception, and they also direct and executive produce Happy Endings. They even have movies to their credits the comedy writing and directing Welcome to Collinwood and directing You, Me and Dupree.
But Captain America 2 is not a TV comedy; it is a big, gigantic, huge tent pole movie with an already established 2014 release date.
When Marvel was looking at directors for the film Vulture got a look at the short list which was all guys, of course. Here's a quote as to how the president of production Kevin Feige of Marvel Studios makes his decision:
“Kevin is a ‘vibe guy.' He likes to see if he gets along with people before he’ll decide about spending the next two years with them. And apparently, they hit it off with Kevin in the room.”
Welcome to the world of dude directors. How can women compete at all?