It was that size because all nav and weapons delivery imagery was superimposed on it when in various modes - steering cues, dive angles, pullup cue, etc. It was very useable, but first generation. The size made it less cluttered and very understandable for dumb bells like me because everything was not all pinched together in a smaller space. It did seem like you were playing on a Radio Shack TSR 80 or Frogger due to the colors though.
The imagery in the model is not really as detailed as in the real one.