Because there used to be a single coherent narrative of "conventional truth" called "mainstream media". Sure it had a lot of propaganda in it, and was fairly heavily controlled politically, but it took a long time for that propaganda to be discovered and acknowledged. By the time it was enough time had passed to say "oh sure, back then there were lies but only other countries put lies in their papers now".

Then the internet fragmented that, providing real time alternative narratives, around the same time that 9/11 and the wars afterwards happened. So people got very interested in the news and it was very obvious that the mainstream news was lying right now.

Now your entire worldview start falling apart, how do you know what's true and who's trying to kill you? You need to find someone else who can tell you what's happening. You aren't quite sure how this whole "critical reading" thing is supposed to work, never learned that stuff in school, but you did find some trustworthy folks who are a lot like you online who seem very confident about what's happening. Even more like you than the old people at the newspapers, and more certain about things, which means they are more likely to be right! This is great, now you will be safe and you actually understand what's happening, unlike those people who keep making things so bad.