Why, though?
FR's the one that your average person is going to know, its the one with the massive amount of popular games to it (With only PS: Torment being an exception), its the one with the known books, its the one that can freely admit any of the various new races and stuff, its the one that an average person would think "Ah yes, Dungeons and Dragons" about.
Greyhawk's only appeal is to the nostalgia crowd. It doesn't have any draw over what FR can do, plus every time someone suggests adding in new player option I'm told this'll destroy everything that makes Greyhawk Greyhawk and we should just be fine with the default four (And maybe gnomes if they're feeling generous)
"You can't play as the fun player options that people specifically want to play and enjoy playing" is not what I'd call a good draw