They are so stubborn because with Apple it's always been my way or the highway. That's led to some excellent integration and good design choices, and I feel the balance has always been about right. And you could choose to opt out when you wanted to (Adobe being a classic example of interface heresy).
But now they're missing the forest for the trees, er sandbox. Sure it's secure, but it's also leading to an iOS model of proprietary file storage. Lame. Nobody in business or serious work is gonna swallow that. Sorry. And we need innovators: many utilities and system tweaks are, face it, better than what Apple designed.
And just take MPlayerx as an example: it's a standard. Puts QT in the shade. But it's gone from the store. Meanwhile, Apple has let in ACRES of video dreck. App after app that's nothing but unsupported video conversion that the developer hopes to make a few cents off of before it disappears. Go look. It's UGLY. Ultimately this is making the MAS into the software edition of the Dollar Store. Kinda odd for a business that sent to Italy for the stone in its retail stores. Can they get a store manager that has a clue?