A lot of developers want portability and retaining all revenue from their programs. Could Apple do even better by providing more for developers on these fronts?
With portability you also get Qt apps, which generally blend in reasonably well on their respective platforms. Developers can go the extra mile to make apps really blend in on each platform, but the defaults are fine.
"For calendar 2017 the App sztores approximate $11.4 billion in revenue was almost 5% of the company’s projected $237 billion in total revenue and over a third of the $31 billion in forecasted services revenue." - https://www.forbes.com/sites/chuckjones/2018/01/06/apples-ap...