Instant for USA banks doesn’t mean instant for USA banking customers, and deposits can be held per fed and banking policies for variety of reasons especially larger deposits. Also, it’s increasingly common to have financial routing intermediaries playing by different rules and non-insured financial accounts that result in no coverage when the money is spent/lost elsewhere and not returned to end customers. Take a look at Zelle case in New York and the nearly $100M customer funds missing with the Synapse bankruptcy.

My point is that these properly designed national systems should also be considered in the USA as well, and not dismissed because something is kind of working right now with a long list of exceptions to a good and safe experience.