Well I'd like to see sources and citations myself. As a maker of flies for fly fishing I can say it is exponentially easier to snip a bit of hair from a skin or pelt than to root around in a bag of loose hair looking for what is needed. Speed counts if you want to make money and grabbing a lock of bulk unsorted hair with tips facing opposite and all directions takes quite a long time to sort out. I'd guess there are easily a few hundred hairs in a quality knot and probably much more. Think of an animal skin like a map of cuts of meat in a butcher shop. On a pelt the hair is presorted by nature and all facing the correct direction. Dead skins can't bite like Badgers are infamous for also. You can't shave a live or conscious Badger, it cannot be done by anyone who likes their limbs and digits.