Now they have millions of cell phones collecting data and the GPS location of everyone offline, they run extremely popular DNS servers to see what websites people go to, most websites (including educational and government websites) include google's trackers so on most websites every page loaded will ping at least one of google servers. They've got people uploading their personal and work documents to their cloud. They are swimming in data collected from sources outside of web search. Between that and the lack of actual competition it's no surprise they aren't investing in making searching the internet better for people. In some ways they profit from search results being terrible. If anything beyond the first few results on the first page is filled with spam and irrelevant websites the top few results to any search become even more valuable.
I think this is exactly why Google's search has become trash. They don't need it. Even when their goals changed from "making searching the internet better" to "Making money and collecting data on everyone" they still depended on search to see what people were doing both online and offline.
AFAICT, quality personalized search results isn't the goal for Google here.
I think the point of all that is generating revenue via advertising sales.
And while providing high quality search results might once upon a time have been a goal, both as a goal in itself and a tool to drive user adoption/engagement, that's no longer necessary as they have a (relatively) captive audience and a (relatively) captive customer base (advertisers). As such, quality search results are no longer all that important.
I'm not a Googler, IMHO, YMMV, etc.