It is the type of infrastructure Russia can not just bomb or shell. That makes it a good defensive position.

Other then that the pipelines continue to Europe via Ukraine. So shutting it down was easy to do for Ukraine before the war. However Ukraine has no interesst in destroying that pipeline as Ukraine has gas reserves in the regions of Ukraine Russia is currently occupying. Having a pipeline to Europe is usefull to transport that gas as well. So Ukraine does not care that much about blowing it up. Obviously if they do, the Russians have no problem shelling them, so they will not do that.

Btw it currently looks like Ukraine is moving to the Kursk nuclear power plant. That has a similar maybe even worse problem for Russia. Especially since two of the reactors are of the same type, which blew up in Chornobyl. Intresstingly there is a cut power line going from the power plant to Ukraine. Having 3GW of unbombable nuclear would be very nice for Ukraine.