My personal theory:
The internet has changed quite a lot in the last 20 years. At the beginning it was almost only nerds on the internet who were running their communities on their free time. Back then there were no algorithms which decided what you see. Everything was sorted by date and recent posts and as such every user saw the same content. So a netiquette developed around that time: Don't post duplicate stuff. Don't double post, edit your post. Read the site rules. Search for information first. No low effort threads. Don't necro a thread without substantial new information. And so on.
That was basic internet netiquette and at least my feeling is that it was universally understood and followed quite strictly. On all the forums, not just a specific one.
I also violated some of these netiquette rules and got reprimanded for it - not by mods, but even by other users. The point is, those were universal internet rules and the whole community was enforcing it.
Then social media happened and changed the way the internet worked. Algorithms were now deciding what you can see. There was no need to actively mod content. On social media the netiquette that ruled the internet had no purpose. And as such people never really encountered that.
Now Stack Overflow is one of the last of its kind where that ancient netiquette still plays a major role. An internet forum which tries to categorize and keep a "clean" library of knowledge. Against a flood of new users who do not know the netiquette. In such an environment mods are the only ones left to remind user of the netiquette. Slowly but surely they lose patience and start power tripping.
It's a case of Eternal September