Thinking more on it, and I wouldn't treat CoD as a great benchmark. Last gen, the series was almost entirely sub-720p, except Black Ops II, and it still drops resolution to cope at certain points. The first Black Ops was so poorly programmed, it was damn near 480p.
It's hard to optimize performance or visuals when a new game is being churned out every single year, and the underlying engine used has only been modestly upgraded over almost a 7 year period. Sloppy, sloppy, sloppy.