It doesn't even make sense in many cases. Bitcoin for example will never be useful as a medium of general exchange, the transaction volume is way too low to support it. Plus its deflationary nature makes it at odds with a healthy economy, where you want gradual inflation to at least exceed the birthrate so there is a hope of lifting people out of poverty.

The workaround is to put everything on exchanges, but then you've lost the decentralized nature of Bitcoin and you are back to just a central database owned by a company, AKA a bank.