With the App Store and iOS 2.0, as well as Push Notifications in iOS 3.0 ('09), Apple created a capability gap between it's preferred proprietary platform and the open web. That gap persists to this day, and is a large part of why we talk about Safari leadership as a historical novelty despite Apple's overwhelming capacity to produce a world-beating browser.
What keeps them from doing it? Strategic antipithy towards a platform it doesn't own and can't tax.
/cc @chriscoyier @tomayac
It seems likely that the success of the App Store was a surprise even to Apple, but once it took root (thanks in no small part to Push, and later IAP), Apple could fully pivot it's web strategy: the leader doesn't need a bridge; best to burn/deprecate it and dig an ever-deeper moat.
This is what Apple has done via its strategic under-investment in WebKit for the past decade.
/cc @chriscoyier @tomayac