Apple is really good in making OTHER PEOPLE'S fabs work for their purposes. Running their own manufacturing was never particularly a forté.
Apple currently really enjoys being on the very latest process node. It's not a given that they could match or improve on that with their own fab (Sure, there is a lot of VLSI design and materials experience, but that does not automatically translate into a state of the art process, and is unlikely to contain the magic ingredient to get Intel back on top).
And in the unlikely case it SHOULD work, that will only invite further regulatory headaches.
