As I understand it:

> A person buys a handheld computer

> I make a program for the computer

> A person downloads the program directly onto their computer

> A person makes a purchase for services within my app on their computer

> Somehow Apple gets 5% of the proceeds, despite being entirely uninvolved except for the initial sale of goods

An analogous situation would be Mercedes-Benz demanding 5% of every ride booked in a taxi they manufactured, for the reason that they have to continue to make and sell parts for the vehicle, and everyone (including the EU) somehow being A-OK with it.