You guys crack me up when you want realistic explanations for a fantasy game in which most of it is not real lol. A game needs to be enjoyable not explainable. For me hunting will be rather boring if all you get in loot drops are mats. I highly doubt rare mats will be dropping from bunnies. To that regard there will never be a reason to kill one or any other creature that will not drop the rare mats. Basic mats will be dropping on everything which means the supply will heavily outweigh the demand.
The fairly inexpensive gear crafted only from base mats will be used (and destroyed) a lot in zvz. Besides, there could be a big variety of base mats dropping from different mobs. This should keep the economy running on demon and human planet. I don't understand how the economy will work on furries planet tho.