It depends what the public seems to be interested in and follows at the time, if a recent movie based in the future came out and in a space of 6 months surrounding that release a game based on the future came out then it may as well get skyrocketing sales. Look at the late 90's to 2005, look at the amount of WW11 movies that came out like saving private ryan or band of brothers and then review the amount of games based on WW11 that came out in that period.
Look, I know I'm rambling and I had a lot more to say but yes, modern war games are the new WW11 but the rule is you can't base them on real scenarios or else the widows or veterans will try to sue you.