Because Apple only guarantees so many phones to the carriers and keeps the rest for itself.
I'm sure the carriers get more as time goes on and Apple get more shipments. But I doubt Apple will give the carriers out of their opening day or pre-order stock.
Ordered a 64GB Space Grey 6+ AT&T.. Won't be getting until October according to my ship date
Ordered my space gray iPhone6 64 gb at about 3:12 EST. No problems from AT&T and the order went through. Now I check my email and my delivery date is Oct, 12-31! So pissed. Stayed up all night to order and still have to wait more than a month? Will never do this again.
Why??