Because nobody else can pilot one.
Seriously do you guys think operating the most cutting edge piece of human technology is easy? Flying a fighter jet is notoriously difficult and only a few elite humans on the planet can do it. They need to train and specialize every day in order to reliably pilot the jet at supersonic speed while dogfighting other jets.
Just think about how hard it is to drive a car. Go up a few steps to complicated machines like cranes or forklifts. The average person can’t control a machine like that without some training. Now go up a million steps and you have the Iron Man armor. The only reason Tony can pilot it so well is probably because he built the technology so he has an understanding of every aspect. He also practices every day.
That means all the credit in the world should go to James Rhodes. A lifelong Air Force member, he was born to fly and dogfight. That’s why he is the only person able to pilot an armor other then the person who invented it.
Thoughts? Do you think it would be easy for Black Widow to master jet aircraft piloting without any prior experience?