This never occurred to me as a reason but makes so much sense
“The accuracy of the search results was reduced, which meant that users needed to do two or three queries to the get the results they would have seen on the first page. That increased the number of ads that could be shown”
Cory Doctorow on how we lost the internet https://lwn.net/SubscriberLink/1021871/4bec46993258f6b7/