California by itself is bigger (by population and surface area) than all of NZ, to say nothing of the rest of the US. I'm not saying that the US has done a great job with internet access, just that it's not exactly a fair comparison.
Having more people in a bigger area increases the aggregate expense, but also provides more people to spread it around (and the US also has a higher per capita GDP.)
There may be legitimate differences that make this harder for the US that aren’t simple failures, but you haven’t identified one.
