https://www.nord-stream.com/about-us/

Gazprom owns 51% of the shares.

Imagine what would happen to US-EU relations if it turned out US did this? Are you sure, even if they wanted to, that they'd take the risk? On a pipe that's effectively not in use anyway. Is it important enough for the US to risk relations with the EU? The US has done more than their fair share of dick moves over the years, but when have they sabotaged an ally?