User blog comment:Crazy sam10/CoDWiki News - July 26 2015/@comment-24.222.156.212-20150728012609/@comment-1187559-20150728092059

Thing is, CoD did the shit out of WW2 (as did many other series of the time) and now they're doing the shit out of future warfare since all 3 studios are doing it, and there's not enough time between them to have them feeling unique. If they went back to WW2, and it was popular, then all the other devs would hop on that hype train and we'd have WW2 up the wazoo again. Frankly, the only era they haven't covered is 1950s-2000s. While Black Ops was here, it was only for 1 game before they moved on to the future, and Modern Warfare was set in a fictional near future at the time of its release, so that one doesn't directly count.

But the devs themselves seem to be having more fun making these futuristic games than they are WW2 games, so I really doubt they'll go back and end up making a game that we essentially already know the story to since it's historically locked.