Why are New Zealand houses so badly insulated?
Insulation is more of a luxury than a necessity in the oceanic climate. If you don't have insulation in a continental climate, you'll die. In NZ, it will be uncomfortable, but you'll be ok.

Dunedin may provide arelevant counter argument. It gets below freezing often there. I don't know about insulation rates.

My second answer is: We're just tough mate. Harden up.