Because shutting it off makes the Russians the obvious bad guys

Why would it make them look like the bad guys when it's the west that has established crippling sanctions that seeks to put ordinary Russians in grinding poverty? It’s all the US actively killing Russians using US hardware, including Russian civilians, and yet you think shutting off the pipeline under the condition that it would be restarted if all this hostility stopped makes them look like the bad guy?

but wrecking it and pointing fingers at the Americans as the ones responsible gives them useful political leverage?

What audience exactly is this supposed to give them leverage with when the entire western media instantly blamed Russia and censored any other narrative? Isn't the simpler solution that the US or it's proxies did exactly what they said they were going to do given they have the most to gain from this, especially with the growing circumstantial evidence that they were responsible?