iCloud is paid for by the users of it. So not anything there as you the app user is covering the iCloud fees. Plus by more developers using those tools means more people are willing to pay for the iCloud service.
I was talking about CloudKit.
Here is a list of other things you get included with Apple's commission fee:
- we developers get up to 1 petabyte of user storage via CloudKit 100% free. Bear notes app does this and they manage 0 servers for their subscription-paid users.
- we could submit 1000 app and app updates in a year which translates to Apple paying about 1000 man-hours worth of paychecks at about $30/hr or ~$30k for app review
- we have free access to using Apple Maps instead of paying Google tons of money to use their mapping API keys (for those high volume users). this saves Yelp and Facebook a ton of money as well as small developers.
- we get many more new features every single year via the SDK compared to Android (like ARKit, Core ML, SwiftUI, Vision, etc... just to name a few).
- we get global distribution for free (including China, you know, where Google Play doesn't exist. also developers generally have to setup their own servers in China because of the great firewall, but if you used CloudKit, it just works without any extra setup).
- we get app store curated editorial with a chance to reach front page in front of 500 million customers a week.
- we have no credit card fees or international taxes to worry about
- Apple provides support to customers asking for refund for an app and app store support in general
- Testflight service is free (for public and private testing)
- app store automatically creates many different binaries of our app and distributes device-optimized versions to each customer. a 1 gigabyte app with many different permutations of versions across hundreds of servers around the world means Apple is hosting about several terabytes in the cloud for us from one single app
- push notifications/push notification sandbox servers
- Web SDK version of cloudkit/mapkit so that you can use it for a web version of your app
- Apple sign in
- Mac notarization service which improves trust by the user for downloading an app from the web
- yearly major releases of Xcode with new features
- analytics dashboard and crash reporting
- and the list goes on and on.
(from MacRumors forum user farewelwilliams)