I don't know where you get this impression from unless you're only looking at what's currently (or recently) shipping. They've always used both and played them

I don't know where you get this impression from unless you're only looking at what's currently (or recently) shipping. They've always used both and played them off against each other. Which vendor is used for a given model changes from one year to the next, although sometimes there will be long stretches of seemingly only using one or the other. There've been plenty of times over the last 15 years where one or the other has been predominant in shipping products, but it never lasts more than a couple years. There've also been plenty of times when the currently shipping product line featured both vendors.