Who said invading was not a big deal? Nobody said that.
If they plan to ever sell gas to Europe again, they'd have to pay the fines most likely. This does avoid the fine issue by sabotaging their own pipelines in a way that can be fixed later, at a relatively trivial cost, and it adds confusion into the situation for the allies.
Russia can now say: we can't turn the gas on even if we wanted to, we're not to blame, and we don't have to pay any breach of contract fines for it being off.
If they plan to ever sell gas to Europe again, they'd have to pay the fines most likely. This does avoid the fine issue by sabotaging their own pipelines in a way that can be fixed later, at a relatively trivial cost, and it adds confusion into the situation for the allies.
Russia can now say: we can't turn the gas on even if we wanted to, we're not to blame, and we don't have to pay any breach of contract fines for it being off.