Think of how often a TOS shirt got torn to shreds. They even joked about that cliche in Galaxy Quest. Trek uniforms were always flimsy and very rarely did they use those excursion jackets. The Khan style uniforms looked like they could take the most beating, and the wardrobe dept did get a lot of mileage out of them. Supposedly some of the uniforms originally created for Khan were still in use through Trek VI, although they were fraying by then.