Big quote: “I think their search engine is the best. Look at what we’ve done with the controls we’ve built in. We have private web browsing. We have an intelligent tracker prevention. What we’ve tried to do is come up with ways to help our users through their course of the day. It’s not a perfect thing. I’d be the very first person to say that. But it goes a long way to helping.” – Tim Cook
Setting an application as the default for a given file type ensures that the program is used more frequently. The same goes for choosing a default search engine. As more people are encouraged to use Google by default, there will be more searches made. Google is currently paying Apple quite a lot of money for the privilege of being the default search provider.