Russia is also not a single actor. There are factions, and they have different interests. The "liberals" aka the economic bloc in the administration - who know full well what kind of shitshow is ahead in the long term - would prefer the war to die down, and for gas to start flowing again, preferably in exchange for dropping sanctions. Because of that, they're a potential threat to the war faction; think of how some parts of the German military repeatedly tried to arrange for secret negotiations with the Allies for an example of how it could materialize. But if there are no pipelines, the "liberals" have no gas to offer in exchange for concessions even if they somehow manage to stop the war and remove the war party from power. This makes their platform less attractive.
(To be clear, this is all just conjecture. The factions are real enough, and have motives that could make players in this game, but it's obviously not the only viable explanation.)
I find this the most likely scenario too. Blowing up the pipeline cemented that Europe wasn't going to get Russian gas for the winter. It left less maneuvering room to any interest groups that could've used it as a bargaining chip as Europe was heading into winter and many expected widespread heating and power issues, some local authorities in Europe even planned for possible mass evacuations of vulnerable population. Gas was the most valuable concession that anyone in Russia could've made. Pipeline blew up and that was off the table. Nobody knew at the time that winter 2022/2023 was going to be exceptionally warm and in hindsight it's easy to downplay those fears and percieved value of the pipeline.
(To be clear, this is all just conjecture. The factions are real enough, and have motives that could make players in this game, but it's obviously not the only viable explanation.)