I am sorry, but I am going to assume you have no idea how making semiconductor manufacturing works. You cannot just turn up one fine day and decide to make a chain of semiconductor fabrication plants. Assuming Apple decided to invest $50 billion in manufacturing their own chips and managed to hire the leading professionals in the industry, and everything went smoothly according to plan, the first chip off the line would probably be in 2018 at the earliest.
Their best bet is to acquire a semiconductor fab company. Unfortunately for them the only two that has the capacity to produce 200 million ~100mm2 chips are Samsung and Intel. TSMC is already way over capacity and struggling to meet demand from Qualcomm, AMD and Nvidia. One of the reasons Tegra 3 is still at 40nm is because there simply is no capacity at the latest 28nm process tech. I know TSMC are investing heavily in 20nm process and it is likely they will start making chips for one or two of Apple's products. Maybe they can handle iPod touch. But iPhone and iPad? No chance, not for many years.
I think much of this decision has to do with the growing popularity of Samsung in the smartphone market. Their growth rates are through the roof and it is a simple matter of choosing themselves or Apple. I suppose if Galaxy S4 and S5 continues this trend they would have no choice to boot out Apple in the coming years.
You're right i have no idea, was simply an idea i mean they have gone at it alone before with bits and bobs was thinking maybe they might do it with this, don't want a flame war was just a idea