Says who? Your Econ. 101 book?
You flippantly decide that no new class of asset can ever come into being and decide to present it as one of the fundamental laws of nature?
Also see this video: https://www.youtube.com/watch?v=8iNeXCAM_Ik
Just to be clear: bitcoin (or some other existing or future crypto) could become for example a currency one day. But it clearly isn't one now.
It used to be a currency quite a while ago - people would actually use it in contracts, most importantly long term debt contracts (long term contracts is where the value/acceptance of the currency really shows; imagine taking or issuing a 30yr mortgage in Bitcoin, as in the homeowner is obliged to pay fixed X Bitcoin per month, lol). A big part of the great depression fighting/relief was to make debt contracts denominated in gold unenforceable.
(And please spare the tech; people really do understand it, at least to the level that matters)