New Zealand has/had plenty of predators, they were just all avian [0], [1], which hunt by sight, and during the day [2]. Existing/nesting on the ground with good visual camouflage is a adaptation to avoid avian predators. Obviously it doesn't work that well against mammalian predators.

- [0] https://en.wikipedia.org/wiki/New_Zealand_falcon - [1] https://en.wikipedia.org/wiki/Haast%27s_eagle - [2] exception here being the Ruru (an Owl)