WW2 is the most used topic for video games because it was basically the last war that had truly clear cut lines of "good" and "evil" (notice the quotations).
Modern wars such as the gulf, vietnam and Iraq wars are not as easy justify and most would argue that they are hardly as entertaining as WW2.
Also consider technology/ war machines. WW2 was the sweet spot really. It wasn't just cannons and swords and horses like past wars, but then again, it wasn't just mindless, relentless bombing and political sabotage like later wars. WW2 was a massive war with many factions and technologies all working with and against each other and that is what makes it an exciting topic.
In the end though, I agree with you, it has been over done and I think it is time to move on.