When they really need to. But they'll fight it hard! Apple's business model is to lock everything down -- very closed indeed. This does not align with the goals of bitcoin, at least, how I perceive them.
tl;dr Apple = closed. BTC = open.
Yeah, Apple has a closed business model, but it doesn't matter. When other important companies will accept bitcoin, also Apple will do it

I don't know when Apple cooperates with Bitcoin I think bill gates will not accept bitcoin because bitcoin is a way to get money illegally in my opinion and bill gates are very honest and hard-working people