This is not limited to cryptocurrencies, e.g., gold-based currencies cause people to "waste resources" mining.

Yes, the 'mining' metaphor was well chosen.

In terms of that gold analogy, what we are talking about in the context would be if gold spontaneously generated itself in proportion to the amount of existing gold and automatically buried itself at whatever depth makes it barely worthwhile to dig up. That waste is the unavoidable cost of making bitcoin-style cryptocurrency have ongoing inflation.