The same reason we have troopers walking into unkown villages in 20-120 deg heat down a stretch of road that had a dozen IEDs the day before that will probably have at least that many today. For the guys next to them.
That being afraid of the NCOs is a bunch of crap. Sure there was some that could breath fire and scare the rest of them but it's a level of respect, not fear. It's amazing what you can get done with respect instead of screaming. The best leaders aren't the loudest, they were fair. Hell, even Patton was known to sit down and talk with troops one on one. Yes, he could swear up a storm and was short tempered, but he was also smart enough not to if he didn't have to.
The Russians had to motivate at the end of a rifle, and we know how well that turned out.