system
A chat on subreddit /r/NoStupidQuestions
human
How tf do these absolutely critical pieces of infrastructure not have armed guards or something? If you try this shit at an airport they’ll send you to Guantanamo. I personally feel like power is just as important as airplanes but what do I know.
gpt
Simply because armed guards are expensive and - until recently - unnecessary. These substations are scattered all over the place, and frankly no thought has been given to security. They've been targets for a while, but usually just the odd lunatic or drunk guy who was just looking for something to shoot at - minimal damage, locally inconvenient if something difficult to replace broke, but that's it.

Recently, however, substations like these have become soft targets of interest to the kinds of people who gleefully speculate that a week of darkness might spark a race war. There have been well-made instructions created and circulated among these groups, and as mentioned higher up in the comment chain, there have been multiple successful attacks that haven't made much of a splash in the news - until the North Carolina one. That's unfortunately bad news, as that attack can be seen as having had an impact for almost no risk to the attackers. So it's gonna happen a bunch more. The good news is some relatively cheap (read: not armed guards) precautions could make these attacks much more expensive/risky: cameras and sand bags. Sand bags to make long-distance shots difficult or impossible, cameras to record anyone coming close to carry out the attack. It's still pretty easy to pull off, but it renders existing strategies obsolete and would likely give authorities more to pursue in the aftermath.