Why CBDC’s won’t be built on third party ledgers

I’ve been hearing a lot of chatter than the Chinese CBDC will be built on xrp ledger or VET ledger and that the US Fedcoin will be built on XRP ledger. All of these scenarios are extremely unlikely because it poses a large risk to the government for these scenarios to happen.
Regardless of what consensus mechanism you are using, it is still consensus, meaning that if you get enough of the miners/validators/node holders to agree, you can still change the protocol and punish bad players. Countries are not going to put up with the risk of their monetary or foreign policies being influenced by this.