1) Priors. Russia loves their clandestine operations to kill somebody or blow stuff up in europe. Be it weapons depots in Czechia or bulgaria, poisoning opponents with radioactive materials or nerve agents your various russian intelligence agencies are there for you. This happened recently, not some cold war stuff.
2.) You are forgetting to include the possible downsides for getting caught in your analysis.
* Russia: Basically none. They blew up their own pipelines. Strange, but they have done stranger things. They will deny it anyway and nothing would come of it.
* USA: Massive. The whole alliance against Russia would crumble over winter and Russia would have a much easier time evading sanctions. Anti US sentiment in europe would go through the roof.
Yes, it could have been Poland or the Baltics but 2:1 my money would be on Russia to sow discord, fear and distrust. Just think how fast that Biden statement was presented as proof for US involvement. Russia right now needs to try and reduce financial and arms aid to Ukraine, any economic considerations are probably secondary. Not saying that would be a good strategy, but that hasnt prevented Russia in the past.
