Why retire her?

[miraja2]

If they brought her back next year she would probably still be a very good horse who could rack up some G1 and G2 wins. Of course, the same was true of Rachel Alexandra and she was retired too.
Most owners, including Zenyatta's, are probably too concerned with their horse's legacy to actually risk losing more races.
It is really too bad. If they actually did that and tried to win the DWC with her, I'd probably be cheering for her for the first time ever.