I see you haven't heard the story.
Well, Bruce wasn't picked because he was "too chinese for the american public" according to the fuddy duddy studio execs.

Carradine got picked as a result instead being of the famous Carradine family and having a willingness to do the part. Bruce apparently was not happy.

At least that was the angle the Lee family put on it and as well was Linda's explanation in the little part of the biographical (sort of) movie of Bruce called "Dragon".

This is all just hollywood news. But it is known that Carradine was unknowledgeable until after having the opportunity to study with Kam Yuen sifu (3rd season MA choreo director) and David Chow (earlier Choreo director and renegade Siu Lam Monk in one episode)
peace

Kung Lek

Martial Arts Links