I think that the title says it all.
Forty years ago people thought that antiques were a profitable investment. It was driven by a high demand for antiques, so people started looking at antiques as an investment. This was based on the "bigger fool theory", which was that you would buy the item solely as an investment, possibly paying more than its intrinsic value, and you hoped that there was a bigger fool out there who would pay you more money for it. The problem is that somebody is left holding the bag when demand goes down. This is a characteristic of many financial bubbles, the first of which started with tulips. https://en.wikipedia.org/wiki/Tulip_mania
The problem with crypto-anything is that it doesn't have an intrinsic value and the value is only driven by hype. As long as the hype continues, you can make money. But crypto doesn't have a use case that justifies its existence. Instead of being a useful alternate currency, it has turned into a get-rich-quick scheme.