It still seems like you’re confused about what’s being paid here. There is no per seat / per developer / per engineer fee. "A developer" in this context means

It still seems like you’re confused about what’s being paid here. There is no per seat / per developer / per engineer fee. "A developer" in this context means an individual person, not an entire organisation. An organisation pays $99/yr to publish on the App Store. That covers all their developers, whether they have one or a hundred. In addition to that, you don’t have to pay anything to be a registered developer. It’s free to register as a developer. You pay the fee to publish on the App Store. Apple having "20 million registered developers" doesn’t translate into the vast sum of money you seem to think it does. The income comes from the number of organisations publishing on the App Store, which is surely far lower than 20 million considering there’s an order of magnitude fewer apps in the App Store than that and publishers can publish many more than a single app with their account.