You should ask survivors of ship fires about wearing man-made, melting clothing, next to the skin. Some still have the shirt on now, 25 years after the Falklands War.
The Royal Navy now only issues cotton clothing, but in the 70s it had become fixated with appearance, so had ordered polyester shirts that needed very little ironing.
Given the choice between cotton and man-made, why buy the item that you know will not perform well in a fire, whether in a plane or a car?