All the commentary I read from reputable media seem to boil down to "Putin did it because that is the sort of thing that Putin does", without providing any further analysis on why it would make strategic or tactical sense for Putin to do so.
The more serious journals such as Foreign Policy seem to have ignored the issue entirely as far as I can see.
I think this video is articulate and sensible: https://www.youtube.com/watch?v=hk-0qJXyido
But the theory presented in the video hinges on the idea that if the americans were to have done it, they would've chosen a more covert means to do it - aka, undetectable (such as cyber warfare).
For example, they would've done something similar to Stuxnet to sabotage the iranian nuclear material processing.
However, i cannot imagine what method of covert sabotage is possible for a pipeline. If everyone believed the pipeline is working, even if it was sabotaged, then they will behave as though it wasn't sabotaged (until they realize it actually is broken). So the effect of the sabotage won't be felt until they turn back on the pipeline, by which, it is too late to for the sabotage's effect to change policy!
So i don't completely buy that the americans aren't a culprit, based purely on the operational design of the attack.
However, i do buy that the risk taking vs risk adverse behaviour does fit. America would not want to risk fracturing NATO from such covert activities. They gain very little - as the pipeline is already closed, and financial and diplomatic pressure on germany is enough to keep it closed. If russia wants to use the pipeline and prospect of cheap gas to lure germany out of the alliance, they've already showed to have failed at it. May be it will change in the future (like 5 yrs down the line), but that seems to be very far to predict, given the current risks of being discovered in between that time.
Lastly, the idea that Putin would covertly destroy the pipelines because they are at a state of war does seem a bit plausible - he's trying to remove the pipeline from being used as a negotiation leverage by any potential successor in ousting him! If germany could sponsor a political opponent in russia with which the gas and economy of russia could be rescued, they might get popular support. This removes the possibility, despite hurting russia in the short term (they're already lost the ability to sell gas from the pipeline, so blowing it up doesn't hurt as much). Coupled with the deniability, the kremlin could blame the act on the US, and hope to cause fracture within NATO for some added effect.