This is not a mystery. The US has the most to gain from this: increase Europe's energy dependence on the US by literally forcing Europe to not use cheap Russian energy
Exactly. And where do you think at least half those billions of government money has ended? In the pockets of all involved in the building them. And no new pipes are being build now. Not very profitable for the oligarchs, isn't it?
Why these unknowns didn't blew second pipe of NS2? It is moderately possible that it was done to pressure Germany to open NS2 (and it may happen next year, nobody knows how future will be shaped). This will legalize NS2 and then Russia can repair 3 other pipes (and repair corp will pocket half of the funds, again).
Also legalizing NS2 will pave the way to building 3rd and 4th pipes in the Turkey system, which Kremlin want very much. And builders of these potential southern pipes will do what? Correct, they will pocket half of the money.
There are a lot of moderately probably arguments for Russia doing it, and all involved can profit from this - Germany, Turkey, Kremlin, Russian builders and gas oligarchs. Sure, Russian people will be poorer, but when it was ever a consideration of Kremlin? :)
And we're talking about 50 meters of a pipeline several hundred KMs long. It's a trivial repair job compared to the effort to build the pipeline and its economic value. It temporarily changes the calculus but doesn't change the long term picture if Germany still wants to buy gas from Russia.
Plus, it seems likely to galvanize Europe into becoming much more of an independent actor. Destroying a major energy source is pretty far over the line of how you'd expect allies to treat each other. It would be a dramatic step and thus far the response has been pretty drama free.
Because these are our client states. NATO's purpose is to bend Europe's will across the Atlantic and away from having mutually beneficial relationships with Africa and Asia.
They aren't our allies; they are our client states. The European leaders align with what Washington wants, and not what the majority of their people want. The US doesn't have allies... only interests.
We are crushing German industry; this is beneficial to us, because it allows our industry to thrive and helps reshore production. We get to sell more energy to Europe; this is beneficial to us... and so on.
Russia risks what? Gas they can't sell anyway? Their incentive to stop the war?
The US risks NATO by blowing up Germany's energy. It's completely insane.