One thing about diversifying your game is that most often a player will do this during the offseason. You don't have time to diversify your game and get all the reps it will require to get a new move, stop or new range become a reaction instead of having thinking about it during the nba season/postseason. You have to get to that point of just reacting, especially for Yao who is not as athletic or fast. If he continues to play for the Chinese basketball team and/or having to rehab from season-ending injuries he can't develop these add-ons to his game. Also, as to the "why doesn't shoot more jumpshots" questions? Teams have figured out that if you just slightly shift his balance a bit, his percentage goes down. And when you are 7'6" with 280+ pounds, it is easy for a defender to hide a small side push or elbow to push Yao off-balance enough to miss that shot.
