Maybe its their plan. To protect their valuable income from other third parties and others (Amazon, Google, Tencent, Embracers etc) buying them and potentially locking them out. I mean it wouldn't be a bad thing if Sony and Microsoft kept their recently acquired studios IP's (current and future) multiplat between them.
Also they have a high profile studio now that has a lot of experience in making successful FPS's so if it all goes down with CoD they have something to fall back on.