You left out the best part:

"The result was the most monumental non-nuclear explosion and fire ever seen from space," he recalls, adding that U.S. satellites picked up the explosion."

Also:

"When the pipeline exploded, Reed writes, the first reports caused concern in the U.S. military and at the White House. "NORAD feared a missile liftoff from a place where no rockets were known to be based," he said, referring to North American Air Defense Command. "Or perhaps it was the detonation of a small nuclear device." However, satellites did not pick up any telltale signs of a nuclear explosion.

"Before these conflicting indicators could turn into an international crisis," he added, "Gus Weiss came down the hall to tell his fellow NSC staffers not to worry."

They used to do good work before, didn't they? Now, it's just blowup the thing. No more intelligent covering of their actions.

Politicians change, sometimes abruptly, especially during crisis. This prevents the "new guys" from starting the pipeline.

Ukraine is still pumping Russian gas to Europe through their own pipeline and are being paid by Russia for it

They could sabotage their own if they really wanted to, or just switch it off.

For Ukraine, it's better to confiscate NS as a compensation for the war, so it better to keep it off and intact, until it will be Ukrainian.

Because Ukraine isn't going to get caught committing an act of war against NATO in Europe while fighting an existential war for its own existence against Russia while completely dependent on supplies from NATO.

The obvious answer here is going to be the correct one: it was Russia. Specifically Putin: Russia can be rebuilt on gas to Europe if it ceases the invasion, but Putin specifically won't survive such an event.

Ensuring his potential successor can't "make a deal with the West" is exactly his sort of thinking. With a side benefit of people asking questions like this right now (I mean, this is catastrophic for him long run, but so is the entire war so it's also on brand with his incompetence).

Nord Stream 2 is (politically) dead in Germany, reviving it is a total fringe position in German politics. And: Putin doesn’t currently deliver any gas through it or Nord Stream 1 anyway. Gas storage in Germany is still filling up, gas prices are going down and it looks like getting through this winter will be tough but it also looks like there will be no dramatic gas shortage in Germany. And all indications are that while things are though, it seems as though there is enough flexibility to move away from Russion gas and that has, if anything, only accelerated. I more or less expect things to become easier as time goes by, not harder, with this winter now looking to be only a bump in that road.

In that current favorable climate for anyone whose political goal it is that Germany does not rely on Russian gas I see no strategic value at all in sabotaging Nord Stream 1 or 2.

You don’t need to blow up Nord Stream 2 if the position of the German government and the largest opposition party is to not move forward with Nord Stream 2 anyway. That would only seem to unnecessarily complicate things (and sabotage can only ever really delay things, better to actually also have the political will align with your own).