Earlier this month, Microsoft introduced three new Lumia handsets including the high-end Microsoft Lumia 950 and Microsoft Lumia 950 XL models. Also unveiled was the entry-level Microsoft Lumia 550. The Lumia 950 XL will only be offered by the Microsoft Store, while the Lumia 950 will be an AT&T exclusive. Microsoft decided to go in this direction even though the other top U.S. carriers were said to be interested in both models.
No matter how strong Lumia sales might be in any given quarter, Microsoft makes more money from the licensing of its Android patents to manufacturers of Android phones. There are some who believe that Microsoft is purposely stacking the deck against success for the Lumia models, so that the current regime can start from scratch and produce its own Microsoft Surface Phone.
source: WindowsCentral