[Qworg]

There's a chunk of Americans who don't have bank accounts (or could work a government account online), so standard methods may not work for 100% of the population.

Also, the Fed is very leery of destroying commercial banking in the US via postal banking or a direct CBDC - I'd expect (if we ever do go that way) for there to a hybrid model. Under that system, banks provide the services to support a digital dollar, while the Fed works through them.

As for "why blockchain" - there's no real reason if the Fed is going to do the work/be the source of trust.