That annoys me too - I mean we have this emergency helmet which deploys over our heads when the canopy is breached - why can't it incorporate a "smart screen" and have the hud info on it?
I know the reason why... It has to do with similar happening during the war (World War II and later) and how a blown out cockpit is stress for a pilot as he has to fly by the seat of his pants.
I don't like it as it doesn't make sense in a sci-fi environment, but there you have it.