It looks like all of those are full Y fares, i.e. the most expensive fare you can buy on that route. Each flight has 9 or more seats available, including the ones on that day that are priced less. This suggests that NZ is just setting the price high by not releasing seats in the cheaper fare buckets. Same thing is happening trans-Tasman. To your point about dynamic pricing, I don’t believe NZ has it, e.g. no matter how many times you search it’s not going to set a browser cookie to charge you more.