They needed to hire a "real" actor, not some autistic spaz to make a movie. Movie sets are absolutely insane.
I had the opportunity to work in movie set building on a location shoot once (Pieces of the Heart Places in the Heart, something like that, with "Gidget") and even ME, with all my other experience, self-controls, blocking-skills, etc, had a rough time with all the distractions and I was easily overwhelmed by all the activity.
If I was an investor, backing a movie project, my money would go to the "good bet."
I knew little about Clare Danes, before I searched, I am always impressed when I see someone who has made it on their own, instead of being a second or third generation actor who owes most of their success to Daddy's or Mommy's previous successes.