Of course individual situations can be different, but this is discussion about the "generic situation".
And this is the best app on the store, a less costly and freer competitor hasn't emerged.
And I can't even sideload my own apps.
This is because it's much easier to earn money on the long-tail dedicated fans than the masses. Especially when those masses are likely to hate advertising based models with a passion.
iOS has more paid apps, for one because people that can afford a high end phone are more willing to pay for $99 for an app.
Look at the pricing for the same app on Android vs iOS.
The cost of sending your app through automated processing and serving it to 99 people needed to make back your fee is probably on net less than a penny.
Offering this service to small time developers would still be 99.99% profit so there would be no reason to make up for lost profits.
I don't think there's nothing getting in the way of Apple charging a very high rent for Amazon's app and a very low one for a random vegan recipe app.