$99/year isn't small. There are 2m apps in the iOS App Store today. Each app must pay $99/year. That's $198m/year as a passive income stream for Apple.
Factor in 30% of app purchase price, plus 30% of in-app purchases, and you have a significant revenue stream.
This assumes (incorrectly) that every app is released by a different developer with their own account. In reality many of those 2M apps are basically shovelware - with developers releasing dozens if not hundreds of different apps under the same account.
Factor in 30% of app purchase price, plus 30% of in-app purchases, and you have a significant revenue stream.