I think "The Greyhawk Wars" began with some dubious decisions made after the new buyout owners of TSR let Gary go.
First, it was publishing the most desirous product for Greyhawk, Castle Greyhawk, as a schmear and mockery of him and his work, and then not owning up to it when the fans grew angry.
Then, it was publishing a different setting in '87 as a default fantasy setting, Forgotten Realms (which only received mixed reviews until Salvatore's novels turned popular and Jaquays Savage Frontier)
- I would add Greenwood's "Waterdeep and the North", a popular and defining supplement, but around me all I heard was how it cloned so many ideas directly from Greyhawk. (Assumed almost certainly from the top). That was not a nice time.
Next, it was the changing of all Gary's IP. The AD&D ruleset was revamped top to bottom and put out as 2e, which has lived in infamy even as the book was easier to read. Due to this, conflict in the community was more than at any other time I remember.
But here is the real Greyhawk Wars. TSR then overwrote all Gary's IP rights in Greyhawk point for point. A 30-page document not unassumingly called "Greyhawk Wars" was published more than tweaking practically every blurb written for Greyhawk in the Catalogue.
"From the Ashes" is a different setting by a different author. Another hit on Gary by a company that bought Greyhawk when it was commercially as popular as Forgotten Realms was in the 90s.
The divide ruined the fan community for the setting. From '89-'95. FtA is not at all a bad setting, but the design instincts were all different. TSR had seemingly forgotten how to design settings for D&D as a game and it became more of a novel writing bible.
In the end the fans were as blasted as Gary, regardless of side. And Greyhawk was discontinued at Forgotten Realms height, which had subsumed it by then. (As did so many other new setting boxes from the early 90s.) And perhaps worst of all, the great newcomer who wrote Greyhawk at that time left the company and the hobby.
Things were at an all-time low by '95 and the end of D&D actually felt like a real possibility. Many unmentioned acts had led TSR to become a trainwreck.
The very first thing Wizards of the Coast did after buying TSR was publish a 3rd version of the setting. Ostensibly calling for the war to be over. (Unfortunately, by that time the field was largely empty).
I don't believe anyone wants to relate the history of the Greyhawk Wars for fear they will start again. Many complaints from both sides were legitimate. The personal grievances were real and likely remain. PLEASE DO NOT REKINDLE IT.
Being in SE Wisc I didn't actually get into Greyhawk because this conflict started shortly after joining the hobby. It took until years later for me to become a real follower, but I was lucky enough to listen to many knowledgeable others about it at the time. Now it's my favorite setting.
Last thing, why is Greyhawk so difficult to change today's game? Well, the history for one. But also because it was the house organ setting for AD&D. D&D is a setting building game, a requirement of play (by original design). And I always say Homebrew is the default setting. But Greyhawk is like Traveller's "Third Imperium", really everything in the core books are for Greyhawk alone. All the secrets, mysteries, personality, and idiosyncracies of the game are from Gary the artist.
By 4e this default setting recognition has largely changed. 5.x needs a setting of its own. One that resembles all the pieces players would presume are possible in it by default. No need for more grievances.