Some of what you are seeing is marketing of course. If you can sell someone a patch of hair for each pattern they tie that results in more sales. Having said that, some patches of hair lend themselves more readily to a given use than others. If you only rarely tie compaduns you can do the job with any hair you have that is the right color and a little more fussing. If you tie a lot of them getting the short hair with longer tips will make things easier and save a lot of time and headaches. Similarly spinning is easier with longer hairs with short tips. I mostly use hair from deer I have helped butcher and I keep batches from different parts of the animal selected for both color and hair length/texture. The hair I buy is mostly died and I want long spinning hair. If I can't select it myself I get hair labeled for spinning from a supplier or brand I trust.
I can think of few acts more selfish than refusing a vaccination.