the US thinks if it fixes a problem that all fifty states have but only fix it in a handful of states that it has solved the problem one hundred percent

meanwhile the citizens go “We have to start somewhere this is a great thing!” and the leaders never get criticized sometimes the opposite people vote them back in

then that is all you hear until the issues reach critical because everything was quarter assed at best

this is how abortion, cannabis, all kinds of insurances, education, food assistance, etcetera already are played in the US

and at that point the citizens and the states are to blame for why things suck so hard

“well they should have voted better over there it is their faults that state sucks!”

which drives us further from solutions

To your first point. This more closely follows current software development methods. Get the core service stood up and out to a set of users, then flesh out the more advanced features. Most of the states in the first round have no state income tax to deal with.
This. Usually we're bitching about the feds just ignoring basic development principles and making shit up as they go along like there wasn't 30 years of hard learned lessons to lean on; this is the first time I can think of where what they're doing actually makes some sense.

After the rough healthcare.gov opening, Obama started a couple of initiatives to work with software devs to bring more modern software practices into goverment, including starting some “software incubator, but for goverment” style groups.

This is likely a direct result from that effort.

That was one of the prime examples of why the gov is starting small and staging rollout