Hmm, there is a palpable difference between "because I was there I get to write the account of what happened" and "Because I was there I decided the course of events," right?
I might, for example, fight and defeat some massive and looming creature, but keep it a secret so that I can cart of its horde of treasure before anyone else knows. Because I told no one, NPCs and others operate as if they don't the monster existed, or if they know it was there, don't know it has been killed and so don't act on the death. That doesn't actually change that the monster was killed, however. Anyone who wanders into its lair while I'm out organizing a treasure hauling caravan would luck into an unguarded horde despite my efforts to keep the secret.
If no one finds out, the world will go on as if the event never occurred, except that I'll have that treasure and the monster will no longer be a threat, so even in my best case the world still responds to what happened in the form of me having more resources and the ecosystem adjusting the monster's absence. These changes will be felt even if their source is not understood.
I didn't dictate history through my lie of omission, I simply obfuscated it.
The same scenario works if a great evil or threat rises where no one saw it, doesn't it? Say this monster is actually the nascent form or avatar of some dark power from another plane. No one knows it's there in its lair, growing more powerful by the day, and so life goes on. I show up and try to kill it, but it kills me, instead. Thinking I might return someday, I tell no one. But in the meantime, it grows to the point where it can properly house the true power of the extraplanar being it represents and stalks out from its lair to wreak havoc. Completely unaware of the threat, Elyria moves on, until it's too late and this thing is eating cities, or turning children into Kypiq, or whatever other dark schemes it might have in mind come to fruition. And maybe even then all we hear at first is rumors, rumors we might ignore as ridiculous tales until the beast is at our gates and it's our kids turning into squirrels.
I admit some bias here based on my own consideration of how world narrative should function, but I think that in terms of world legacy, imperfect knowledge among the world's denizens is actually pretty important, as it helps to influence the course of events that is the central narrative thread of history to evolve along believable lines.
I feel that, if we messaged major events to all players equally, you couldn't ever see a single hero rise up, for example - you would see the world organize outside of the game so that everyone could take organized action in-game to address the event, even though that's just not how events flow in real life.
Now, that doesn't mean that clues wouldn't be there to be seen and acted on - there's a difference between forcing awareness of an event on people and providing the cues needed for players to become aware on their own. Perhaps that monster's rise sparks ill omens across the world, for example, or perhaps the dangerous wildlife in the area starts to diminish and dwindle as the monster feeds, so that people can become aware that something is happening out there. Whatever the messaging method, hints do have to be there so people can realize a call to action has been raised and respond to it.
And, in the same vein, allowing you to visit those events after the fact doesn't exactly work, either - you might make choices differently than the choices that were made at the time if you played it yourself, which can't really propagate out to the rest of the game. That sounds pretty unsatisfying to me, but the idea of just "recording what happened" and letting you watch it like it's a TV show doesn't actually sound much better to me. Some "arcs," for lack of a better term, could take in-game years to unfold, leaving you with large swathes of "security cam footage" to review in order to find "the important bits," if that analogy makes sense.
Anyway, I'm rambling, but those are pretty much the thoughts behind why you find me in the "let the world unfold, even if no one is there to be watching" camp.