Because if Google doesn't, then it could see its search monopoly evaporate. The vast majority of rich people in the world use iPhones. In the US/Canada/UK/Aust

Because if Google doesn't, then it could see its search monopoly evaporate. The vast majority of rich people in the world use iPhones. In the US/Canada/UK/Australia/Japan and many more rich countries, the iPhone is the most common device - and even within those countries, the iPhone's demographics skew wealthier. iPhone users are a ton more valuable to advertisers than Android users - they have more money and they're willing to pay for premium things. Let's say Apple switched to Bing. Most users won't know how to change their search settings so Bing will now get 90%+ of iPhone search traffic (and the most valuable search traffic). This puts rocket fuel into Bing's ad business. Advertisers don't just think Google and nothing else. Suddenly, Bing is potentially more important since iPhone (and Mac) users that they want to reach are going through Bing. This has big implications for Google's ad business beyond just traffic loss. When we're talking about bidding, more bidders push up the price. It's not just about losing the iPhone's traffic. It's also about losing the ad bidders on the other side. If you're a monopoly on search ads and you lose 30% of your search traffic to a competitor, you are probably losing a lot more than 30% of your revenue. This is because part of your revenue exists due to people getting outbid. Let's say that you and I are bidding for the "laptop" keyword. You bid $1 and I bid $2 to outbid you. Google gets $2. If I decide to move my bidding over to Bing, you get the laptop keyword for $1 and Google's revenue is halved for that keyword - and they're only getting 70% as much traffic on top of that. As traffic shifts, bidders will shift. As bidders shift, the amount paid for the traffic still coming to Google could decline in addition to their traffic declining. So it's not just the loss of Apple-device traffic. It's the loss of bidders that drive up the price of ads even when they lose. And this has knock-on effects for Google's businesses. If Bing's search ads get this rocket fuel, they start getting the attention to take on Google's ad business for publishers. Google has been steering searches to their properties, but all of a sudden Bing could start steering searches to Microsoft owned properties. Maybe LinkedIn figures out how to get people to post videos in a YouTube-competitive way - and with the most valuable traffic being steered toward those videos. Yea, LinkedIn is supposed to be professional, but it's kinda lost a lot of that over time with random click bait already. Being the default search engine is a powerful position. You might say that you'd use Google no matter what and we're on HN so you probably know how to change the default search engine. Most people would just end up going along with whatever the default is. Google rose to prominence via their search results, but people aren't feeling as happy about Google's search today. Google has kept their dominance by paying to be the default search engine for almost everyone - either by paying Apple and Mozilla or by paying engineers to create Chrome (and putting a lot of marketing money behind it).