If you study trial practice you will learn that one of the jury's main complaints is that lawyers are to repetitive. They say that the same point is made over and over. It is understandable. From a trial lawyer's perspective, you want to be sure that the jury "gets" a particular point, so you beat on it over and over.
The defense may have decided that any point Zimmerman senior would make is already made. It is a total judgment call.
one more person who is an ex-judge would not be one too many
Plus by having the jury remember Zim’s mom and uncle when they think of his family it reminds them that this man is himself part black. Mom and the uncle are darker than Obama or Tiger woods.
The prosecution based much of their fabrication on casting Zimmerman as a sheetwearing clansman.