The main assumption here that's wrong is that government is competent at IT. It's not.

Even giant companies have a really hard time integrating new IT infrastructure. A failed IT upgrade is one of the most oft cited reasons for firing CEOs, for example. Incidentally, this is why Costco refuses to upgrade their systems. It's too costly and the chance of failure high.

If you want to know how bad it is, just remember what happened with healthcare.gov. Government is an order of magnitude worse than large companies. CBDCs and the dystopian nightmare you're talking about is almost an existential risk to government. Think about some software bug that doesn't let you buy groceries or pay for a used car from a neighbor. It's bound to cause way more strife than almost anything else. This is why despite the power to do so, China is rolling out their CBDC slowly and very carefully. Even then, there are going to be big glitches.