Why wouldn’t Zimmerman benefit from taking the stand himself; I know the defense normally puts the accused on the stand only when there is no recourse, but it seems to me he would benefit from taking the stand. He is attractive, articulate, and has a consistent story.
As I said, when the the defense is decisively winning the case, you don't take any chances no matter how small. Don't give the prosecution any chances or openings to trip up the defended.
Furthermore, for example, the Florida Casey Anthony trial. The prosecution had a very strong circumstantial case against Anthony, however, the defense did not feel the state’s case against Anthony was strong enough for her to take the stand. Anthony never did and she won. Taking the stand for defendants in murder trials can be a high risk move.