While it might seem natural to turn by rotating the body to the side you want to turn to, it doesn’t help you when skiing. It forces the hips out of the turn, making it difficult to get on the edge of the ski. Finally, this makes it harder to engage in the next turn, because we then have to rotate the upper body all the way to the other side now, and every time we do big movements like this with the upper body, we defy our balance.
Core strength as well as hip stability and leg power will help you get rid of this bad habit.