If you have ever watched a muffler shop bend some tubing ...its usually a 90 degree bend .Their machine is not setup to make curves. Then there is the problem of how to cut a piece of tubing two times the length of it. I would imagine that fenders are stamped with dies and a flat piece of metal. Hard to duplicate and have it look nice. If you were real talented you could probably make some with an english wheel but as cheap as they are ,it would seem to be alot of work for very little results.....Just my 2 centavos