There's a few factors involved, and I don't claim to be able to provide a very intelligent analysis... so apply that filter to my reply here.
We in NZ were *incredibly* lucky that we have a left leaning government, who is deeply invested in looking after people, ahead of profit. So despite the inevitable massive cost to tourism (massive earner for NZ), they decided quickly that we were shutting the borders hard and fast, and fund businesses to close everything non crucial for a month. It was unbelievably easy and fast for businesses to get funding, to be closed. So, much of NZ had a paid holiday for a month. Apply various disclaimers that it wasn't perfect, and some businesses folded, and some people lost income.
Then I think fundamentally NZ (as a collective, not every single individual) thinks very differently from how USA (as a collective, not every single individual) thinks as a society. USA appears to be very focused on freedom for the individual. "I have a god given right to do what the f**k I want, and the overall good of the people around me as a community can eat a massive bag of dicks". For example: I want a machine gun, in fact I want 100 machine guns, because FREEDOM. The fact that this directly means a lot of complete psychopaths will also have machine guns, well, that's tough luck for the community in general, because I will have my FREEDOMS. NZ still has a fair share of people who want big guns, sometimes because they're psychopaths, sometimes because they like guns. NZ society has gone "No. No, we don't need machine guns, because the only thing you hunt with those are human beings". So, nobody gets machine guns legally. Then we had that mosque shooting nutjob white supremacist (I'm not going to name him, he's not worthy of having a name). A month later, massive crackdown on gun rules. Government buyback of guns. Because the greater good needs to be served. Then there's free public health. Again, not perfect, but look at the number of people living on the streets here, or dying untreated on the streets here, because of medical bills, compared to USA. It will be a number as close to zero as you can get. Because that's what serves the greater good. Enough of NZ agreed, for the greater good, we're giving up our FREEDOMS, because there's a global pandemic, and fuck it, we don't want to kill everyone's grandma.
So, again, with huge amounts of disclaimers applied, that this is just the opinion of one not particularly well educated Kiwi, it appears the difference between the USA and NZ during the pandemic is better leadership, and more focus on the greater good than on individual freedom.
Time will tell if we screwed the pooch or not. At this point in time, it appears we here have come out better, through a combination of better management, and better luck (geographical isolation, no land borders, low population).