I have to go with Zummi and Declan on this one. She was ranked #1 and is the winner of 2 US Open titles and a Wimbledon mixed title. Who really knows why her career wasn't longer. Sometimes I think it was by choice as much as by injury, though I don't question her injuries at all.
Being so focused and so driven at a young age is indeed a scary thing once you've been removed from that situation. For instance as soon as Chris Evert retired, she felt relieved at not having to be that person any more. Not that she was a bad person, but to be at the top you have to be so single minded and there's just so much more to life....especially the people in it. Even Hana came back from her break from tennis with a much different personal outlook that helped to prevent her from ever seriously threatening to reach the top again.
My point is, maybe in all that time away, Tracy was happy. I've read her book and I think its clear that she missed tennis, but she enjoyed her fame and fortune and the opportunity to do so many other things as well. She would have had to give up so much to get back to the top. Maybe I don't know what I'm talking about, but I think its possible. I also think that its not a crime to feel that way if indeed she did.