Because you teach alot of things in life and music is a love. For me coached my son's bball team for 6-7 years and I treat him like the other players. If I were to do that with music, he would hate me even more. You yourself know when a student practices or not. Imagine your child living in your house and you keep beating on him to practice. He will hate the instrument even more.
That is why I don't teach my kid or told others how to teach him. They are on their own.