you retard. Since he already has a full-time job (and then some) he needs someone at cabinet level to oversee the military. Maintaining civilian control is essential like Truman said. That's why Truman = good, you dumbshit.
Yes, civilian control of the military has always been essential, ever since George Washington stopped being a general and started being a President.
In the short 200+ years since then, we've become the most powerful nation on Earth, militarily and economically. Obviously the way we've been doing things works. You want to cede military control to the military? You are asking for a coup.
Think for once.