Our main problem is that there are two different groups of health experts, the CDC (which said reasonable intelligent things that would have stopped the plague) and the WHO (which said whatever China’s government told them to), and in the absence of a “consensus” among health experts the politicians were allowed to do whatever they felt like.
Also New Zealand is an island nation that can literally just quarantine itself completely, which would never be a viable option along america’s borders even if we could shut down the ports.
“Why doesn’t a continental superpower with thousands of miles of permeable land borders and overland trade just do what a small isolated island nation whose primary trade partner is ALSO an island nation did?”