“The voters’ choice will be binding because all of the parties that make up the current Government have committed to abide by the outcome.
“We hope and expect the National Party will also commit to respecting the voters’ decision.
This isn't "binding" in any sense of the word. Its just a politician's promise. And as we've all learned over the last decades (and indeed from this very process), politicians are lying fuckers who will ignore their promises the moment it is politically or personally advantageous to do so - and then lie to you to your face and claim they haven't. Their "promises" mean nothing. Pretending that they do - let alone that they mean something over other parties - is simply an insult to the public.
As for why they've chosen to do this, NZ First hates drugs and doesn't want legalisation, let alone to actually vote for it. As for Labour, while most of them probably want legal cannabis, as with pretty much everything else their inherent chickenshittedness means they don't want to pay the political cost of actually making it happen, preferring for change to happen by magic instead. And so instead of a binding referendum with certainty not just about the proposal, but that it will actually happen, they're giving us a glorified public opinion poll with no certainty at all. And under those circumstances, I'm not sure why anyone should bother participating in the farce.