Imagine a 175-pound racer traveling down a race course at 35 miles per hour, making a really tight carved turn. The course is smooth as a baby's fanny but hard as a rock. The racer's skis are tipped way up on edge. The skier needs that speed to provide enough energy to adequately bend the skis. Because those speeds are way too fast for most skiers, they have to skid their skis before they engage the edge.
Most instructors ski at low speeds during lessons.
I find it curious that over the years, beginners have moved to increasingly shorter skis, but the instructors teaching them have not. The irony is that beginners have skis that can make very neat little carved turns on gentle slopes while instructors don't have equipment that easily allows them to do that. They are using the wrong tool for the job. If those instructors were on 150's when teaching beginners, they might very well teach a different kind of lesson. For instance, because a carved rum is so easy on a 150 cm ski, instructors just might have their beginner students give it a try.