I don't agree that the number of users has no bearing. That is a ridiculous premise. The internet practically runs on page views, and attached to that is adverts which makes things sustainable.
Even if Maps loses money, which is doubtful, the use of maps is not limited to Android. iOS users can and do use it on their browser and more importantly, people can use it on their computer browser, independent of any OS, Ubuntu, OSX, Windows, etc.
Before my smartphone days, mapquest was my go to to print out directions, now supplanted by Google maps. Maps draws in many eyes. Can Apple leverage the same? Can you access Apple Maps through the browser? Google Maps, even if a net loss, which is highly doubtful, undoubtedly plays a large part in making Google an indispensable part of your life. Look at the outcry now that the limited version of maps has been removed. Google insidiously makes their products so useful that you'll be questioning how you got along without it before.
Imagine if Apple created a search engine. Imagine that Apple's search results were comparable to Google's, maybe even a little bit superior. However, the caveat is that only iPhone users and people with Apple computers could utilize the search.
Compare that against Google search which is device independent. If you can connect to the internet, you can use Google search.
Where will the advertisers go? Where will the money flow to?
Android does not define Google. Google Maps does not define Google. Google defines Google. They provide a service.
Apple? Apple's identity is hugely tied into iOS and is largely defined by the iPhone and iPad, with Macs taking a seat in the back row.