Horst gave the example of petrochemicals which he pointed out are natural, but tend to be awful in a lot of ways. The most common chemicals are preservatives and foaming agents. It is a well-known fact that the majority of consumers do not like to buy shampoos that don't create suds. If a shampoo does not produce a good lather, it is considered inferior. Consumers have certain expectation of all beauty products.
Consumers also demand a reasonable shelf life.
Without preservatives many products only last a few weeks. The only shampoo that I know of that does not include a foaming agent is made by Aubrey Organics. The Aubrey haircare products are sold in health food stores and are not found in department stores or hair salons. Aubrey Organics is owned by Aubrey Hampton. He resists the use of sodium laurel sulfate in his shampoos.