Apple has way too much interest and dealings with chip manufacturers lately. Something's amiss. It Seems like they are loading up on capacity. But for what? What is it they think will drive demand to such an extent that they need all these firms cranking out chips.
Not really. Remember they also had a lot of interest in chip manufacturing, even before iOS devices, with their Mac when they switched from IBM to Intel and there was even RUMOURS of AMD as well as creating their own.
IMO it seems they're sticking with Samsung because they have a 14 nm chip and they have the track record of success when it comes to quality and quantity. The others, I feel, are being groomed to either replace Samsung one day or pick up any slack if there are any supply issues in the future. Also as someone noted they could be used to manufacture chips for other devices. As always business is business.