There's another factor here which is the issue of resilience of national infrastructure. By having the parallel systems that is, a faster payment system that runs through banking networks and a digital currency system that runs over the Internet, the overall resilience of the payment system (which is critical national infrastructure) is significantly enhanced. The core settlement networks can, and do, go down from time to time albeit rarely. The near infinite amount of money that would need to be spent to make such systems 100% reliable makes the relatively small amount to be spent creating a CBDC look like pretty good value for money.
There's another factor here which is the issue of resilience of national infrastructure. By having the parallel systems that is, a faster payment system that runs through banking networks and a digital currency system that runs over the Internet, the overall resilience of the payment system (which is critical national infrastructure) is significantly enhanced. The core settlement networks can, and do, go down from time to time albeit rarely. The near infinite amount of money that would need to be spent to make such systems 100% reliable makes the relatively small amount to be spent creating a CBDC look like pretty good value for money.