User blog comment:Damac1214/Call of Duty Vietnam Concept Art Released/@comment-402843-20140626130904/@comment-3967954-20140626134434

They're listening to the buyers. Although the people who want WWI, WWII and Vietnam games are very vocal about it, they're not actually the majority. Historical FPSes don't sell as well as they did ten years go. If this Vietnam game is ever going to be made, then Activision would have to be convinced that a lot of people are actually going to buy it, otherwise it's not worth doing.