Their official reason is to "keep the lights on" in a context of declining gas supply. But its worth noting that Gensis - one of our worst fossil polluters - is directly invested in the gas industry, and therefore has an interest in supporting the governments narrative that our options are basically coal or gas. That simply wasn't true. So they've decided to try and make it true.
(An interesting point: Genesis had consent for an 858 MW wind farm, big enough to replace Huntly, and they sat on it for a decade and then just let it expire. They could have solved this problem and made Huntly redundant a decade ago, but they'd rather burn coal and destroy the planet).
Meanwhile, in reality: we have 1.1 GW of consented and under construction solar, and 1.3 GW of consented and under construction wind, plus huge pipelines of both in the preliminary stages. We should build them. We also added 150MW of rooftop solar in the last year - a decent-sized power station. We should build more of that too. We can fix this problem with wind and solar and batteries, and every MW of renewables we build means less coal and gas burned. Every MW we build means less profits for the ecocidaires in the fossil fuel industry. And the government should be making it a holy fucking mission to drive those murderers into bankruptcy. Instead, it seems that National prefers complicity.