The GPL is not compatible with the Apple App Store because it contains: "You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License." By submitting an app to the Apple App Store and signing the license an author can grant that right to Apple, but somebody that wants to use the code can't do that...

When you're the author, you can publish your code under whatever license you want.

To publish in the App Store some app you've been distributing under GPL, you basically have to give a separate, more permissive, license to Apple.

And what would be the reasoning for that?! It doesn't seem to make sense. It seems like another one of Apple's arbitrary rules.