Yep, on their platform. Just like Wal-Mart and Kroger have full control over what products their competitors are allowed to sell too (in-store versus name brands). Microsoft only makes and sells their games for example for the Windows platform and doesn't allow portability.
As a pattern there's nothing wrong with it.
The crux of the issue is that creation of a mobile operating system that people actually want, like in some other industries, as resulted in two dominant platforms that don't compete all that much with each other. That's a much more interesting and important "problem" to solve than Apple/Google create competing apps on their software distribution platforms.
> Just like Wal-Mart and Kroger
You've been repeating this flawed comparison for years. It's getting really stale.
The App Store is markedly unlike Wal-Mart or Kroger, in that a user cannot buy one thing from one store and another thing from the other. This would be like buying a Kroger-branded car and then being forbidden from entering the Wal-Mart parking lot. The problem with the App Store is not Apple's control over it and the Apple-branded experience - it is the exclusion of alternative and competing schemes that could naturally drive down their own prices.
If Wal-Mart or Kroger did this, they would be in the same hot water as Apple. Probably quite a bit worse, since people understand the commoditization of groceries better than software.
> That's a much more interesting and important "problem" to solve
No it's not. The industry has no interest in overturning it, if there was commercial demand for an innovative third platform then we'd see one. The crux of this issue is Apple becoming a services company and then denying competing services from competing on equal grounds. It cannot get any clearer than that.
My phone that I purchased is not "their" platform. Better analogy would be if Wal-Mart sold me a fridge and then somehow managed to make it so I can only store groceries purchased from Wal-Mart in that fridge. Now if anyone wants to sell me groceries they need to sell them to me through Walmart, otherwise I can't refrigerate them.