I’m guessing that the knowledge of the techniques to support large-scale web search have diffused out of Google - it has been a few decades after all. Not to mention that the distributed system knowledge that used to live only in Google was either published by Google or cloned in other projects, usually made by ex-Googlers. And you can now rent capacity at scales that 20 years ago required Google to build lots of their own data centers.

Also, there is now a use case for paid search APIs - LLMs and agents - that essentially didn’t exist a few years ago. Not sure why Google hasn’t leaned more into this, but probably a combination of Gemini and Ads interests have combined to view their search index as an increasingly valuable asset, when if anything it might be corrupted already by these interests and therefore be less valuable.