Maybe because people don't have unlimited amount of time to keep up-to-date on all data and research on toxicity, negative health effects, safety, etc on tens of thousands of products from a couple hundred countries.
Any product could apply for regulatory approval in the country where it is being sold. If the product does not get regulatory approval, it could be sold in a special shop, so customers are aware that they are taking a risk. That lets customers choose for themselves whether they want to take the risk.