Unless it makes more than 15B for Apple in terms of being able to do something with their own search (advertising?), it is a loss.

Google is paying for Apple to not have the default be Google search. If Google wasn't paying, Apple would be able to offer the default search provider to someone else or make it a user selectable choice in the new phone setup.

Google is paying to keep Apple from thinking about their own provider or shifting the default to Bing.

https://www.statista.com/statistics/297137/mobile-share-of-u...

Organic search from a mobile device is 60% of all Google searches. If we take the 50/50 breakdown for iOS vs Android and apply it there, 1/3rd of all google searches are from iOS.

That's what Google is paying for - making sure that people who don't care about their search provider continue to make up 1/3 of all of their searches (and data gathering).

The next thing to consider back on that "what would the expense gain" ... does Apple have the resources to spin up a 1/3 google data center. I mean, yea they do... but that's expensive and if they aren't selling adds, it is purely an expense.