My thinking is central banks also don’t want the transparency on how and how much fiat they create out of thin air.  The privacy protections got to be asymmetric and the public would need to accept that for this to gain adoption, outside of totalitarian style forcing it down. 

Or CDBC can be limited for international settlements only, but then the value is limited and why do that?  Then again, it is only as valuable as policy prudence and domestic productivity (and military might to enforce), which central bank would want to open the book first? 😂