New Zealander here too. Our country is definitely getting fatter, though people don't believe it and always try to shine America in a bad light, while ignoring ourselves. I loved What We Do in the Shadows, and Taika Waititi in general, but relying on fat jokes is getting old. As you mentioned, Maori and Islanders are generally bigger, so maybe they are trying to make the film more relatable to them. I bet there will be at least one KFC joke in there somewhere.