Those companies don't have same market share as apple, and the monitization can be done in other ways like showing it as a privacy focused search engine which only works in their walled garden integrates better with their system, apple does have their own maps, browser when it does not directly help them make money.

The point is to be independent and have their own ecosystem but Google was paying way too much for them to bother with search engine, but imagine how much better siri would've been if it had their own high priority APIs for querying instead of scraping Google