The central bankers want their own pseudo-crypto currency system. They do not want most of the public crypto systems.
The advantage that crypto has over gold and silver is that it can't be confiscated. If I have Monero, not only is it next to impossible for big data methods to figure out who has what amount, but it is impossible to forcibly seize the assets by forfeiture.
If I have a safe filled with silver or gold, the feds could serve a nonsense red flag warrant, cut open the safe, and conveniently have the assets liquidated and unrecoverable by time I get through with my "speedy and fair" trial that tosses the warrant.
Depending upon what crypto coin you hold, it does hold some intrinsic value. A service token, like ethereum (which I am not a big fan of, but whatever), have at a minimum the value of the service the token is exchanged for on the network - which is distributed and verified computing. For some businesses, that's pretty important.
In the case of monetary tokens, like Monero, the intrinsic value is a share of the sum total of the coins available for transactions. What that means in real terms is variable - but so is the price of rice in egypt.
Central banks like the fad of crypto currencies. They like the enthusiasm around investment into them. They like the illusion that all cryptocurrencies are impartial and can't be tampered with.
But even though bitcoin has open ledgers which can be tracked, any central bank adopting it would Mount Gox themselves in 3 years' time. There are also questions about who gets the keys to the kingdom. Bitcoin wasn't set up with the idea that a whole corporate system would be accessing accounts. No one can take back a bitcoin transaction once sent and if an employee has enough of the business, they can just send a few million dollars worth of crypto to random addresses and fuck everything up. There are a lot of things that even more advanced coins have not entirely solved.