Say no one builds their own, and iPhones now only have first party apps. How many people are going to buy them now? How well did the Windows phone sell with no app support? How's the app support on the Apple Vision Pro?
The idea that devs owe Apple for use of their SDKs and API development is absurd. Apple already profits from it as people by their phones due to the amount of third party app support. See how Apple's profits go when WhatsApp, Instagram, Spotify, Netflix Uber, banking apps, are all no longer available on their devices.
Vision Pro is an excellent example
What Apple really needs to do is mimic their old policy of no fees except for games. Let everyone develop for it, and then rug pull by making the fees apply to everything
But they can’t do it twice. So the Vision Pro ends up with no ecosystem