They aren't forced to use Apple as a distribution channel, just like Lenovo could also not sell computers on Amazon or at BestBuy and they probably make a higher margin when they sell D2C as well.
It's a cold blooded move by Apple, but I don't think its "nefarious". I'm very much against their rent seeking with the app store though.
This more akin to Booking.com placing ads for hotels in an area. The hotel gets revenue and Booking.com gets commission, and sometime advertising recovery fees on top.
Developers of apps should be allowed to opt out of this, or really should be an opt in feature.
They get their 30% subscription fee. And they get to control the customer relationship. App publishers have a really shitty deal here.
Mobile computing would be so much better for competition if this had become a Microsoft / Google duopoly rather than have Steve Jobs with his perverse app store model. We'd have web downloadable apps and a better mobile web.
We now have a cartel for 50+% of American consumers. The cartel is so greedy that it's now placing ads to confuse and ensnare consumers even more.