The more realistic but cynical take, and most likely the real case: Hey, what is left of the original d&d world we can update in a way that will finally get rid of and alienate almost all of the remaining customer base that comes before 2014/2018 or so. I know, what about that super problematic setting? Dark Sun? No, the other one... ah Greyhawk. Yeah let's front cover warrior the crap out of it! That will be awesome! Yeah... mach 10 full ahead!
So, yeah I'm going with take two. A deliberate destruction of everything people enjoyed, related to and connected with in Greyhawk will be purposely and spitefully destroyed, oh I'm sorry "updated". You know, just to show "them/others" from "before" they are truly not welcome any more, at least in any "official" capacity. Love to be wrong, but I don't see why I would be.