I wonder if they're concerned about having too many so-so defensive players. Last year only Cam was iffy in 1-on-1 D (though his team defense was excellent), with Castle, Newton, and Clingan being great to exceptional defenders and Karaban being pretty good.
Diarra is stout defensively, though smaller than Castle. Mahaney and McNeeley, who knows. The former is definitely on the smaller side. And there's no Clingan. Reed is OK, Johnson blocks shots but is easily overpowered.
I wonder if the staff is prioritizing Ball at the backup guard position for his strength and defense over a guy like Brea.