Apple used to have to roll-their-own to hedge their bets. For example, Safari and iWork came about when there was a possibility that Microsoft would pull support for IE and Office for Mac.
Still need people to press buttons though. But I feel too many decisions have to go through a tiny set of people. But I have no insights into the org. I do wish they would do more smaller releases. Like update Notes without a full OS update.
Just focus on a core and let third-party apps do what they're good at.