(disclaimer that I was the TL of Google News a very long time ago, so feel free to ignore what I say as biased)

I would argue that monster.com and craiglist, which collectively removed the majority of newpaper revenue, were probably the nail in the coffin. You can see some of the decline pre-internet in this 1999 take: https://niemanreports.org/newspapers-arrive-at-economic-cros... ... which already laments the decline of journalism.

Pre-internet, editorial boards were fundamentally gatekeepers of knowledge. They were certainly not unbiased, but for the most part they had a level of integrity. Now, one can find (or have pushed) any "narrative" one chooses, whether or not it bears any resemblance to reality. While Google does make it easier to find any/all of this content, I would argue that the intrinsic incentives of social media platforms for more engagement are probably the high order bit.