A primary benefit of Android is that Google is allowed to put their search engine on Android mobile devices for close to free instead of multiple billions of dollars.
If Apple customers are the most affluent and are worth at least $12 billion a year to Google, how much are the statistically less affluent Android users really worth?
How much are customers buying $200 phones worth to advertisers compared to customers paying 3 times as much?
Google also has to pay third party Android OEMs a share of search revenue.
I would imagine a lot of it is mindshare. Apple is trendy and had already called their bluff once and made Bing the default search engine for a time.
Google pays Apple to make Google the search engine on the iPhone for the same reason that Coca Cola and Anheiseur-Busch spend tens of millions per year on 30 second spots during the Super Bowl.
How much are customers buying $200 phones worth to advertisers compared to customers paying 3 times as much?
Google also has to pay third party Android OEMs a share of search revenue.