The simplest answer is most likely the correct one. Who has been causing the most mischief in the last year - Russia. So what you are implying now is Poland, US or Ukraine did this - with might I say no evidence.Why is that ‘obvious’?
The most obvious benefactor is Ukraine, because this eliminates a Russian-German means to bypass them for energy.
People are protesting in Germany and it’s not even October yet.
Poland is an obvious benefactor as well, since they don’t want the Germans to have any leverage to cut deals with Russia. Poland’s new pipeline from Norwegian gas fields opening points to another way this benefits Poland.
The PNAC/neocon crowd running US policy benefit because this prevents the Germans from making any deals with Russia, and makes them more reliant on the U.S.
What is Russia’s ‘obvious’ benefit to blowing up their own infrastructure to prevent the possibility of delivering their gas production? I’m open to examining Russian motives, I’m just not clear what they would be. Why would Russia do this to themselves?
However there are now multiple reports of a Russian war ships in the area by europeans. Why would Russia do it - I gave one plausible reason, they are concerned about the declining natural gas prices and tried to cause the prices to go up. I also think Putin as leader is becoming more unstable.
So lets not do some long diatribe on possibilities. Yes there are possibilities, but the most likely outcome is Russia with the evidence also supporting this.