NS2 was started ten years ago and cost around nine billion euros. Nine billion buys a lot of insulation, heat pumps, and wind turbines over ten years. Wheras NS2 was only ever needed so that Russia can turn off gas for Ukraine without turning it off for Germany.
I think it was more about Germany being able to buy gas straight from Russia without having to pay fees to Poland/Ukraine/Belarus/whoever for transporting gas through their territory.
Poland takes ~200 million euro for 30 bcm (0.15 bcm/m euro) over ~700 km of pipeline [1]. NS2 would cost 9.5 billion while transporting 110 bcm (0.01 bcm/m euro) [2]. It would take over a decade to break even (ignoring maintenance costs or any sort of cost overrun) and the world has been moving away from fossil fuels so it'd break even at a time when nobody wants it.
What is uncanny is how the US started taking notice of NS2 around 2020, with Congress threatening sanctions against Germany [1], and Biden ominously talking about how there's going to be "no more Nord Stream 2" [2].
