First of all, the cryptocurrencies don’t actually work as currency. That’s the big deal. They’re hard to buy because they are deliberately incompatible with the rest of the financial system. They’re incredibly hard to hold on to because, well, something goes wrong it’s “Sorry for your loss.” That’s a function of the irreversible design. And finally, they’re actually really hard to spend. Most merchants who accept cryptocurrency aren’t actually accepting cryptocurrency, they’re using a service that turns it into dollars.