That would destroy the purpose of an analog stick.
If I'm playing a racing game, the right analog stick is my steering wheel. I can hold it at 100% (full lock), 25% for a slight turn, etc. .. how would you do that with a trackball?
The trackball idea is only useful for scrolling a mouse around a screen .. which can be done just as easily with the stick.
Another reason: a trackball requires constant movement to move a cursor where as a stick just requires you to push-and-hold to accomplish the same task. I've got enough problems with RSI .. I don't need my console games to make them worse!
That makes sense.
I'm pretty sure a middle ground could be found though, like a controller with both or one that can swap out a stick or a button that causes it to lock in place and behave like an analog stick vs a track ball.
I was mainly considering FPS's which are by far the most hindered game on the console when compared to there PC counter parts do to that right analog stick though. I find it atrocious just how limiting they are in terms of accuracy in movement and control and speed in turning motions.