Because chemical fiber is synthetic with petroleum and other raw materials.The production of chemical fiber will produce a lot of pollutants, consume a lot of energy and water, and the degradation rate of chemical fiber waste in the natural environment is very slow,so it is generally believed that wearing cotton fabric is more environmentally friendly than using chemical fiber.
Cotton is the crop that uses the most pesticides and 25% of the world's pesticides are used in cotton cultivation, if true, poses the strongest challenge to this view.