Actually, it is about not giving them a level playing-field. I do not know if you have ever encountered the situation I am about to describe, but I personally had to pay close attention to realize it.
In the fruit juice section, for instance, some are governed by the Food and Drugs Act. The nutrition facts appear on the container and there are requirements related to that. Next to them, there are small individual juices which are considered natural health products because they have added vitamins, various antioxidants, and so on. So they did not take the same route as foods. However, they are placed next to food on grocery store shelves. Those juices are being bought specifically for children. I happen to believe it could be harmful for some children to consume a lot of them, because a lot of vitamins and minerals have been added. If children take supplements as well, it may turn out to be excessive.
In my opinion, natural health products have no place on grocery store shelves. They should be kept apart so people really know what to expect when they go to that section and do not confuse those products with foods governed by much stricter legislation.