Because you are an evil, worthless kid?
Please forgive the rude question, but how am I suppose to know the answer to this. As TB pointed out, your parents have their reasons. If you would like to have input on these reasons, ask your parents and post the reasons that they give you here. You can find out what some of us think.
Oh. Your question is not accurate. You are not the only person in the world that is not allowed to participate in this activity. Your questions belies your prejudices.
Jay