Google is intentionally dropping five year old results from the index and prioritizing five hour old results. They have complete control over whether they're doing this. Part of SEO is making five year old results look like five hour old results, which is something that Google did to spammers, not something that spammers did to google.
Google has decided that it is more profitable to make sure that somebody who types "chicken" into the search box gets either chicken restaurants nearby, or listicles and video covering the story on the news today about a chicken that scared away a bear. They've given up on depth.