Equipment question: Why are most boxing/muay thai hand wraps 100% cotton? They take so long to dry and remove sweat. Why aren't they made using wicking, dri-fit fabric as you seen now in gym shirts?
I suspect that this is mainly due to the main function: providing stability and protection. Secondarily, it may be a matter of hygiene.
For stability, the fabric has to stay in place and not move against each other much. While flexibility as such, within certain bounds, is not only tolerable but even helpful for that as you can see from medical bandages used to stabilize joints with traumas, slipping of layers against each other is not.
If you tried to fixate something with, say , a band of silk, and you wrap it several times around really tightly, you'll see that the slightest movement will loosen it and make it ultimately fall off in no time. The same would happen with modern dry textiles, even if not as fast.
That's the main reason why medical bandages, just like hand wraps, still feature a high percentage of cotton and a rather coarse fabric, as it is a good compromise between thickness, flexibility, and stabilisation.
The other one is hygiene: traditionally, you would wash them at high temperatures in order to get rid of bacteria that love sweat and make them stink eventually. If you cannot wash a fabric above 40 degrees celsius and you need more than 65 for that, you have to use other means.