> once they leaned heavy on the ranking

Not sure what you mean here. Google started with PageRank which is a decent, albeit gamable, ranking algorithm. They’ve never not been leaning heavy on ranking.

Mid 2010s, Google began supporting conversational (non keyword) searches. This is because a good number of queries are difficult to reduce to keywords. But it is an inherently harder problem. And at the same time, the open web enahittified itself, filling up with SEOed blogspam. And a lot of user generated content moved into walled gardens.