To understand that, you'd need to know just how bad search was before Google. Search wasn't even a "thing" on its own, it was usually merely a feature of large portals (AltaVista, AOL) which were large, slow, cumbersome and gave pretty irrelevant search results. At that time, search relied mostly on the meta tags of the pages themselves - which was easy to game and lead to a lot of spam in the search results back then already.

Google's clean interface (basically just a search box) was so revolutionary that it's hard to comprehend today - I still remember it took me a few days to even take it serious, it was so thin and lightweight. PageRank was a gigantic step forward in SERP relevancy and even though it was gamed eventually by link farms and paid backlinks, it took a lot of time and effort and the first few years saw few spammers.