I think this is just a symptom of our general move away from the larger parties. Smaller parties tend to (though don’t always) have more extreme views. Labour and National are pretty close in policy, but when you add Greens on the left, they negotiate for stronger left-leaning policies. Then perhaps it would be ok if the policies were outside National’s normal field of vision, but then you throw in Act and NZ First and they each have things that are key to them lying outside the normal box, which they negotiate for.

There is also a worldwide resurgence of further-right wing parties, that thrive on the divisiveness that instant worldwide communication encourages.