While I’d highly recommend giving either the article a read or the companion podcast a listen because Ed Zitron did some fantastic reporting on this, the tl;dr is that a couple of years ago, there was direct conflict between the search and advertising wings of Google over search query metrics.
The advertising teams wanted the metrics to go up to help juice ad numbers. The search team rightly understood that there were plenty of ways they could do so, but that it would make for a worse user experience. The advertising team won.
The head of the advertising team during this was a man named Prabhakar Raghavan. Roughly a year later, he became the head of Google Search. And the timing of all this lines up with when people started noting Google just getting worse and worse to actually use.
Oh, and the icing on the cake? Raghavan’s previous job? Head of Yahoo Search just before that business cratered to the point that Yahoo decided to just become a bing frontend.
Zitron is fond of saying that these people have names and it’s important that we know who’s making the decisions that are actively making the world of tech worse for everyone; I tend to agree.