It is a kitchen sink setting from back when the kitchen sink was much smaller. Some people believe this means one should be restrictive with what one adds to it or changes in it.My man, no one is hating on Greyhawk. The worst thing that has been said about it is that it is a kitchen sink style setting. And considering it includes fun-house dungeons, a literal cowboy turned God, and spaceships with moss aliens and laser guns... I think that is a fair cop, not hatred.
Personally, I am utterly convinced that in the alternate reality where Gary Gygax keeps control of TSR, and where the Forgotten Realms is never published or pushed as the primary D&D setting, but D&D otherwise expands theme-wise in similar ways over the course of time, Greyhawk would look much like the Forgotten Realms does and would have been bent to accommodate every change in D&D. The only reason it hasn't is that it's been on ice, or at least sidelined, for much of the time since Gygax left.