What do CBDC & blockchain have in common?

So I fail to see why CBDC's require blockchain technology.

What specifically about append-only logs that use consensus mechanisms to add entries will enable CBDC's?

Clearly central banks aren't after decentralization so why not keep it all on a single ledger? If they issue coins directly to people, there's no need for banks and so blockchain isn't needed to help reconcile multiple ledgers.

They'll def want to preserve the ability to change transactions retroactively - so "append-only" feature isn't needed either. Anonymity, verifying public ownership, setting hard currency limits etc. - all those aren't needed either. Even smart contracts don't require blockchains should they want to implement those.

Is it all a ploy to use the hype surrounding blockchain to do something they considered for a while?