Because we had seen the same old tricks a thousand times before.
Nobody wakes up some day saying I know exactly how to stop a train without being caught. Or: I know exactly were to cut to enter in this restricted area that normal people never had heard about it just to steal a few copper cable here and there (or worse, fiber optic cable)
Random actions are truly random. This acts aren't random. They need instead planning, precise knowledge that is not available to most people, and direction to coordinate them in several locations at the same time
Do you have evidence that Russia did this ?
At this point, a p-value is more than enough.
Each time Russia is suffering troubles in the war, this events happen; and they happen in clusters. A few models are recycled again and again and adapted to each country. Sabotage to railways and wildfires "caused by climate change" are two of the most popular. Another is sending people to protest and cause trouble in the streets with any excuse, supported by campaigns of disinformation online. Another was cutting marine internet cables. We even may suspect that the lone wolf backstabbing people in the streets (where previous options aren't available) is another.
Just in the last week, Ukraine killed two more Russian generals and a colonel. Losing 13 major generals, admirals and lieutenants and more than 42 colonels [1] is not a minor issue in any war. Ukraine also hit again a big refinery and is pushing Russians in the front lines.
Putin can keep doing chest thumping and faking strength in public, but is obvious that Russia is not doing as well in the war lately, as he would wish. The facts point to a different reality.
You may have noticed the huge increase in Russian provocations to NATO lately. Putin risk to be assassinated by his own generals increases with each general killed. He needs to redirect the angry towards an external target, and is desperate for a NATO move that would justify him (legally and in the eyes of Russians people) to start a major mobilization soon after the Russian elections.
So expect more events like those in Europe in the next days, and maybe some dumb move of Trump to destroy another good thing in US, with the clock ticking before he turns into a burnt out asset.
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[1] https://en.wikipedia.org/wiki/List_of_Russian_generals_kille...