They get a cut of app store sales, and additional third parties pay them to display ads within mobile apps using admob. Although it isn't hard to come up with

They get a cut of app store sales, and additional third parties pay them to display ads within mobile apps using admob. Although it isn't hard to come up with other ways for them to extract more money out of android, I can't imagine a lack of willing buyers for all sorts of information they could harvest from the billion or so deployed devices.