Well most of infinity ward left because of the horrible conditions they were put under
Infinty Ward is making the next Call of Duty ._.
Anyway I think that Infinty Ward do bad campign and storyline while they do good online and maps.
Now Treyarch do good storylies and campign (They have a zombie storyline connected to the campign) but the online is pretty "ehh". If the two were to work together they would make up for each others cons