I don't see why new arrivals are to be treated differently from someone already in NZ who has been assessed as a "probable" or "confirmed" case. But I guess that incoming numbers are down low enough where we *can* quarantine them.
And I think we would be the first country in the world to eliminate covid-19, not just the first western country.
Most confirmed or probable cases in the community were already in an isolation "bubble" (as we all are) with extra requirements to try to reduce spread to others in their bubble - but not expected to be 100% effective.
New arrivals introduced to an (almost certainly disease-free) bubble is higher risk for "new" cases amongst family members.
Ah, I see. So it's about ensuring that uninfected bubbles stay uninfected, and infected bubbles get "clean" within this month. So a newly-arrived infection, especially (nearly) asymptomatic) now could lead to other (nearly) asymptomatic infections in the bubble, and consequently still be contagious after lockdown, and start to spread again when bubbles coalesce.