I get the impression that the contestant coordinators have a different idea of what constitutes "a good contestant" than, say, any of us fans, or indeed anyone with a clue.
All I can add to this is my own personal experience. Last year I went to a Wheelmobile event, was lucky enough to have my name drawn at random, then went up on stage and solved the puzzle.
I was called back a few weeks later for the final audition, solved a puzzle in the first section of the day in front of the entire group, and then passed a written quiz with 16 puzzles on it.
Then those of us who passed were asked to stay around and play a slightly more detailed mock game. I was pleasant and enthusiastic, called out "good" letters in a strong voice, and clapped appropriately for my fellow players, but just couldn't bring myself to be a "jump up and down type screamer". For the record, I am a white male in my early thirties, and am of average appearance. I was dressed in a sport jacket, button down collar shirt (no tie), a pair of slacks, and dress shoes.
I never heard from them again. It is what is, but it was disheartening in the sense that I knew I was a very good player, and yet nothing came of it. And with the process as difficult as it is (having to go to a number of Wheelmobile events hoping you're one of 50 names that get drawn from a barrel of about 500-1000), it has made me not want to try again.