Natural fibres are synthesized from the raw materials that are obtained from nature.
These raw materials include cotton, kapok, and coir fibres originating as hairs borne on the seeds or in the inner walls of the fruit.
Other examples of raw materials are flax, hemp, bamboo, sisal, jute etc. All of these are either plant products or tree products.
So the heedless use of these plant based raw materials for manufacturing natural fibres leads to the deforestation of many forests, thus affecting our biological ecosystem adversely.
As the raw materials for synthetic fibres are petroleum based chemicals or petrochemicals so there will be neither deforestation nor the imbalance of biological ecosystem.
Hence manufacturing synthetic fibres is more preferred over natural fibres as manufacture of synthetic fibres are actually helping in the conservation of forests