It's easier to do customs, sorting and routing all in one place. Rather than routing large international airplanes from China in Alaska, they just refuel them in Alaska and then head straight to Kentucky. After arrival, they do customs, sorting and distribution of the phones to regional planes and trucks. It's actually very efficient, cost-effective and saves time. Alaska doesn't have the resources to do what Worldport does. I've heard that nearly half of the operations out of Louisville are UPS.
Of course, I worked there when Steve Jobs was still dreaming up the iPhone concept(1993-1997).