Suppose ot were true, how would you turn the evidence into profit? Sell it to western media? Let the wrong person know and they'll tip off western intelligence and then your car will drive you into a tree. Sell it to Russia? Maybe they would pay, but would you like life in Russia? Once you're there, maybe they don't pay after all. Or maybe you sell it to Russia, stay in the west, and spend the rest of your life looking over your shoulder.
The proof, if any exists, is worse than worthless.
You mean we don't know who managed to blow up the pipeline that some NATO members threatened to blow up several times? Yes, we only have this official investigation from two ""independent"" countries that wouldn't hesitate to point their finger at Russia if they had any evidence, no matter how weak, yet they closed it "without identifying perpetrators". You're right, no clue!
You can argue that if it was Russia, western countries might want to ignore it, because otherwise they'd have to do something.
Much easier to respond by supporting Ukraine.
For a NATO ally to do it would be extremely risky -- what if the others hadn't kept quiet?
(You can't always predict what your allies will do)
It's worth a lot less in a hypothetical scenario where everyone's decided its in their best interests to forget all about it, which may be similar to the scenario we're currently in.
In politics, the truth isn't usually worth very much, and is second fiddle to the ends.
The proof, if any exists, is worse than worthless.