The argument I remember goes something like this (and I could be remembering it wrong).
They claimed technical problems prevented them from fulfilling the amount of gas required by their contract for NS1 and NS2. Due to sanctions they essentially had to provide gas for free - or at least in exchange for money they were unable to spend or access.
The pipe blowing up potentially saved them from having to pay a penalty fee in the contract once the gas hadn’t been moving for X number of days.
Why would Russia be concerned about a contract? Reminds me of a story on something like Unsolved Mysteries....lady had her husband killed because she was a christian, and thus, didn't believe in getting a divorce, and wanted to be with another man (his best friend.) And his friend went through with it...
They left one pipe of NS2. It would have been a political victory for Putin with humiliation of the German government if they had switched to this instead of stopping gas imports via NS1&2 completely.