I guess AirNZ has done the numbers the loss of of revenue from people selling the tickets is less than the cost to check ID & the increased time (people missing flights & having to play find the bag & slowing down boarding (domestic flights get people through the gate faster than international)).
Moving it to security I don't think would work as none have the space to add another queue. Additionally whose is legally responsible & who is legally allowed to match ID to boarding pass? If is airlines responsibility AvSec would have to increase their fees to the airline to cover it. And the PR nightmare they would have targeted at them as people grumble.