Ok I can not hold from the second reason:
Imagine the system, where central bank is having the ledger somewhere. Where? Be it POW or POS, it will be all computers from central bank against other computers of central bank. Why should stupid system like that exist? Why should the central banks miners or stakers compete against the same central bank? The essence of blockchain is the competiton.
Central bank can well having all the transactions stored in one database (with backups). But that is exactly what is happening now with the monetary base. Same argument that was used against XRP or IOTA for example. But XRP/IOTA can in theory decentralize. Central bank is central bank.
I think the main problem is that we all are forced to have opinions on everything. The only use of blockchain for central bank currency is if they peg the normal fiat currency to the BTC or some other leading crypto exactly as it used to be pegged to gold. But even that is not gonna happen soon.
If you talk to God, you are praying; If God talks to you, you have schizophrenia.