You are wrong about the revenue direction. Apple were a significant provider of revenue to Google for map usage. Below is just the article I picked but Googling for 'google maps ios revenue' brings up quite a number.
http://www.ijailbreak.com/news/apple-ios-40-google-mobile-re...
I suspect Apple were upset at the limitations believed to be imposed on them by the Google contract (no turn by turn) and it was expiring anyway. It was probably negotiated when they had no idea how sucessful the iPhone was going to be. Google probably also wanted more control to insert advertising and the fact the two firms are now competitors in mobile OS's and at legal loggerheads made agreement unlikely.
What incentive was there for Google to back Apple's poor implementations when they can just release their own versions that actually bring the features Google wants to offer their customers on their own schedule, as they are doing now?
Such a maps app is more like a browser visiting maps.google.com - browser vendors also don't pay for doing that.
But what reason would Apple have to go out of their way to maintain their own datasource (and pay other vendors, like TomTom, for help) if Google's data already fit the bill? Even more so if Apple was going to be paid to use it as you speculate. A dislike for Android isn't reason enough, especially as this move strengthens Androids position for the time being. The only logical explanation is that Google wasn't willing to play ball, for one reason or another.
Good example of that weird "Google can do no wrong even though it's a company built on collecting information about users and selling it" nerd mentality. It's well known that Google was increasing it's map fees.
If that were true, they would offer the service for free. As it stands, for normal contracts, only the first 25,000 requests per day are free[1]. If we assume Google wasn't willing to give Apple a special pricing deal, with 300M+ iOS devices in the wild, Apple could easily be left shelling out a fortune each day to user their data.
[1] https://developers.google.com/maps/faq#usage_pricing