DPF wonders why people still vote for Labour, as opposed to the Greens. I think tribalism is a major factor – political scientists think that most voting is expressive (‘I vote for this party because of who I am’) rather than instrumental (‘I vote for this party to have these values advanced, or these policies implemented’) and so people vote Labour (or whoever), because ‘they’re a Labour supporter’.
But a huge difference between the parties is that Labour have electorate MPs and the Greens don’t, and probably won’t have any for some time. Having a well-funded advocate for an electorate who will one day (probably) be part of the government is a big advantage.
There’s a theory that the Labour Party is in decline, destined to be eclipsed by the Greens, and pretty much everything that happens in contemporary NZ politics strengthens that case. But it’s hard to see how the Greens could try to capture many/any electorate seats off Labour without splitting the vote and handing almost every electorate seat in the country to the National Party. (Of course this problem goes away if we transition to a proportional voting system in the electorate votes.)