Vitamins are competition for the pharmaceutical industry.
Vitamins and supplements and other natural health products help people safely and inexpensively. Pharmeuceutical drugs are expensive and can have harmful side effects and you need a prescription. Many people wish to avoid using drugs. Vitamins and supplements and other natural health products could be banned outright so they could not be purchased by consumers, or only sold in very low doses, or classified as drugs purchased by prescription only at a much higher cost. These supplements might not even be carried by most pharmacies.