Everything has a price though. If you offered half of Apple's market cap, I'm sure they'd be changing their tune. (Yes it is an exaggeration, but my point is that there are exceptions.)
The problem lies in that Apple already gets 100% of the profit from being vertically integrated today (so the offer would not only need to be large, but more than what one could reasonably hope to make in return). If it were just that Apple had a really good CPU then both Apple and the 3rd party(ies) would be able to come to the table with a net positive deal, but vertical integration makes it so only 1 party (Apple, in this case) can come out ahead until they are dethroned for other reasons completely.
