I think the headline only asks half the question. I'd argue that no huddle coupled with scripted plays/not giving the QB a lot of options to audible does reflect sizable coaching ego. Cubit also has a bit of a point about coaches doing it purely for stats. If you're a coach under fire or a less talented coach (Cubit would play many of them in his career) you might do it not for ego, but simply because you a want a stat that will get you noticed, save your job. Assuming you can't get the wins for whatever reason, a valid fallback is to try to excel on one side of the ball that gives you a bargaining chip come the offseason and the coaching carousel (something to the tune of "Hey, I'm an offensively minded coach and my offense kicks ass, I just need money for a new DC, don't fire me Mr. Athletic Director!").
that is nice bonus change