Russians made a lot of money from German needs for natural gas, and Germans needed lots of natural gas. By severing the pipeline, Germany was entirely cut off from an economic basis for diplomacy with Russia, and by extension so was the rest of the EU. This could have served as a diplomatic off-ramp, but instead served the same impact as sanctions on Russia: both sought new sources for critical trade resources.

Plus, it was found that the US and Ukraine did it.