I don't understand why Russia didn't do this from the very beginning.
I'd guess that they were not confident in their offensive power at the start.
AFU was much stronger, there was a chance of NATO joining etc.
At that stage, if they struck critical infrastructure, it'd be repaired by now. And the 200k troops sent by Russia at the start have no chance at beating the 800k-ish forces from Kiev in 1 go, electricity or no electricity.
Either you can believe in the glowie narrative that "Ivan is drunk and stupid, he doesn't know he sent too little troops to win at the start to Kiev, he doesn't know that it's possible to attack infrastructure etc.". Or, Russia just did a very convincing impression to make the world including Kiev think they're going for the whole country at once, allowing them to take the most critical strip of land in the South with minimal losses and hold it until AFU has been degraded sufficiently.
There are some grains of truth in that Russian politicians are truly just as corrupt as the ones in the countries Yeltsin modeled the system on. There are also incompetent commanders. But the long delay on any form of infrastructure fight until the start of winter tells us that it is some sort of strategy.
If it was incompetence based, you'd almost certainly see sporadic strikes from day 1 but they either don't reach the targets or aren't repeated enough to matter.
Due to how much control there is on the NATO side of the Internet, a lot of people on both sides started to think Russia is on a strict timer to do stuff. That is likely completely different from how Putin and his commanders see the war.
Awhile ago some glowie on twitter posted that Russia lost 1900 officers during the war as a major gotcha moment, only they were preying on misinformed people, because a modern army consists around 20% of officers. If months of war were ongoing and Russia lost less than 10k (just going off the glowie numbers, personally I think Russia lost more, but its impossible to know due to thick fog of war) +, then that is a rate Russia can sustain forever.
Just like during the Iraq invasion NATO was not in a hurry, they can take months letting the Iraqis and Kuwaitis duke it out, keep bombing civilians until the country became demoralised and depopulated etc. If you were there you can say "why is Bush not going in with tanks and massed air on day 1?"
Russia shows no signs of being in a hurry to rush in with everything they have either.