Because defaults matter for people that simply use what is given to them. Also, those payouts have addition benefits. Given the billions they give to Apple, I'm

Because defaults matter for people that simply use what is given to them. Also, those payouts have addition benefits. Given the billions they give to Apple, I'm pretty sure that it prevents Apple from developing their own search engine, or from blocking ads in Safari by default. Same for Firefox. Google's Search is still the best, though. And I don't have any numbers, but I could bet that it's by far the most used search engine even on browsers that don't have it as a default (e.g., Vivaldi).