D coaches typically like the trench warfare and physical issues, the repetitious grind, the hand to hand combat fundamentals, and the manly part of the game. O requires organization, coordination, skill development, timing, movement execution, and innovation. (A lot of things are shared by O and D such as scheme development, play calling, teaching details, and instilling positive emotion, work ethic, and discipline). I think the required O skills are a little more in tune with the head coaching required skills, but a D coach can certainly possess or learn the head coaching required skills.
I was considered by most others as an O coach and learned or possessed the required skills to head coach. I assure you that internally I was a D coach.