Because text matching was so difficult to search with, whenever you went to a site, it would often have a "web of trust" at the bottom where an actual human being had curated a list of other sites that you might like if you liked this site.
So you would often search with keywords (often literals), then find the first site, then recursively explore the web of trust links to find the best site.
My suspicion has always been that Google (PageRank) benefited greatly from the human curated "web of trust" at the bottom of pages. But once Google came out, search was much better, and so human beings stopped creating "web of trust" type things on their site.
I am making the point that Google effectively benefited from the large amount of human labor put into connecting sites via WOT, while simultaneously (inadvertently) destroying the benefit of curating a WOT. This means that by succeeding at what they did, they made it much more difficult for a Google#2 to come around and run the exact same game plan with even the exact same algorithm.
tldr; Google harvested the links that were originally curated by human labor, the incentive to create those links are gone now, so the only remaining "links" between things are now in the Google Index.
Addendum: I asked claude to help me think of a metaphor, and I really liked this one as it is so similar.
``` "The railroad and the wagon trails"
Before railroads, collective human use created and maintained wagon trails through difficult terrain. The railroad company could survey these trails to find optimal routes. Once the railroad exists, the wagon trails fall into disuse and the pathfinding knowledge atrophies. A second railroad can't follow trails that are now overgrown. ```