It appears that, besides having titles of nobility, at least these few people actually had real class.
“Von” implied they were part of the old Prussian nobility, and Hitler, although he needed them, despised them.
Hitler hated (likely jealous of) the aristocracy, especially the landed nobility of eastern Germany and Prussia collectively known as the Junkers. Hitler's contempt and mistrust of his general staff is well known. That many from Hitler's general staff conspired against him after he rolled the dice a few times too many is not surprising.