We're talking about billions of pages and if not ranked (authority is a good hueristic), filtered (de-ranked), etc then good luck finding valuable information because everyone is gaming the systems to improve their ranking.
I think this is part of the reason you get a lot of fake news on social media. It's a constant stream of information (a new dimension of time has been added to the ranking, basically) that needs to be ranked and with humans in the loop, there's no way to do this very easily without filtering for noise and outright malicious content.