Part of the problem with supporting Greyhawk is that the fan base was factionalized from TSR's actions in the late 1980s.
Forgotten Realms has the blessing and continued participation of its creator. Most other game worlds were created by committee, with no one person having the key leadership role, with perhaps the exception of Weiss and Hickman when it comes to Dragonlance. Even Eberron has it's creator actively involved.
But Greyhawk suffered from Gary's departure. And also suffered because TSR decided to put an "experimental" stamp on the world. Something GH has never recovered from. It started out with crap like the Rose Estes novels and the "joke Castle Greyhawk". Then came "Greyhawk Wars"--designed to shake things up. Afterwards, other writers started to treat it with some respect, but the damage had been done. And some people even disagree on who should be a factor in keeping the game system alive.
Wizards obviously looked at the fact that GH names were used in spells, etc, as well as the lack of success of GH products compared to the other lines, and decided to make the campaign more generic. Because of the factionalization of the line, and the fact that 3e changed some of the rules for characters as well, GH became "generic D&D world". I think Greyhawk's weakness and factionalization of its fan base made this the most palitable decision--Realms and Lance had a lot of novels and more published material that they didn't want to contradict, it would be too much work to create a generic world, and the other worlds had specific quirks that weren't "generic D&D fantasy".
I don't think there will ever be a true consolidation of the GH base. Gary's Castle Zagyg, if the project can ever get completed, will likely satisfy those looking for the legendary dungeon adventure, but he is unlikely to ever return to GH development since he hates the current D&D incarnation. Writer Carl Sargent, like Roger Moore, appears to have retired from gaming. Erik does his best, but he is limited by what he can do officially.
Personally, as a publisher, I wouldn't want to touch this world with a 10-foot pole, because of all this controvesy.