Simply I've never been interested in it. I've been always finding history of modern wars much more boring than earlier times. Because of that I know almost nothing about this period (even though lately I watched documentary about WW1 and it was quite interesting). It's just my personal preference, nothing more
But I would gladly play early medieval or antiquity game (Trojan War would be cool, though I'm aware that lack of knowledge would be problem). Also science fiction BoP is my little wet dream, but it would terribly difficult to host I believe. On the other hand I would vote against setting in player-created world (like Iropia or Estia) - such games are in most cases terribly incoherent and history of world makes no much sense. Despite that, of course, as I've said, I'll play anything set before 1850, be it historical of fantasy.