Exactly and they know this.

The biggest market is mobile now, and people on mobile don't open their web browser on their phone and start typing google.com before they search for something like people used to do on desktops 20 years ago, but they search for something directly in the built-in browser's address bar whichever search engine that might be, as most people stick to the default on their device whichever those might be. Defaults matter.

Apple could probably switch the default search engine in Safari to anything else and most users wouldn't bother changing it back to Google unless the results were to be absolutely terrible.