She's even less of a character in the Ultimate Universe.![]()
Sharon Carter has a role to play in Captain America or it's sequel. They could have put Carol Danvers (Ms Marvel) into SHIELD for the Avengers movie (like in Ultimate Universe) or Bobbi Morse (Mockingbird). Even Jessica Drew could have worked. All of them have much longer comic book histories and are unlikely to be staring in their own movies anytime soon.
I just think there's not much room for the Maria Hill character to grow in a limited set of movies, and having Cobie playing someone with the potential to be a superhero in a later movie would be more exciting.