Of course they aren't. But if a handful of random gamers on the internet can come up with an explanation that doesn't destroy the setting, including gamers like myself who have never played in the setting, then why should I believe that game designers who have played it, have researched it, and potentially have a deep love for it, are incapable of doing so?
IF you want to make the argument "It is possible WoTC could screw this up"... well you are correct. IT is also possible a new disaster strikes the global market and the bookd doesn't get published at all, or that WoTC does an amazing job that everyone loves and praises for being a work of genius. All of our crystal balls are showing the same smoke, despite what we may say.
Have you read the PHB entry on Goliaths? Here is the version from the playtest.
Towering over most folk, Goliaths are distant descendants of giants. Each Goliath bears the blessings of the first giants—blessings that manifest in various supernatural boons, including the ability to quickly grow and temporarily approach the height of the Goliaths’ gigantic kin. Goliaths have physical characteristics that are reminiscent of the giants in their family lines. For example, some Goliaths look like stone giants, while others resemble fire giants. Whatever giants they count as kin, Goliaths have forged their own path in the multiverse— unencumbered by the internecine conflicts that have ravaged giant-kind for ages—and seek heights above those reached by their ancestors
Now, this does state that Goliaths go their own way, but it also makes it clear giants and goliaths are kin. They bear the blessings of the first giants (the giant gods) and they have giants in their family lines.
Now, when I go look up "giant" in Greyhawk wikis...
Giants are found throughout the Flanaess, though the vast majority of giant populations are concentrated in and near the Yatil-Hellfurnaces and Corusk-Rakers mountain chains. A Giant's environment generally depends on which race or subrace it belongs to.
And that is it for the majority of them. Though Canonfire goes into more detail, and ALSO points out that Goliaths were added to Greyhawk in 3.5. So, if the setting rarely decided to go beyond "Frost, Fire, Storm, Cloud and Hill giants live that direction" then it isn't hard to also add "Goliath" to that list, because they've already mashed and mixed the giants up, so one more to the mix doesn't change anything. I am giving them EXACTLY as much detail as the other giants got previously.
Or the Horned Society, the ones who worshiped Devils? So, you have Iuz's Evil Kingdom of Demon worshipers for Demon-blooded Tieflings, the Horned Society Devil worshipers for Devil-blooded Tielflings... and gosh it is so hard to figure out how Societies that worship devils and demons might end up yugoloths, the evil mercenaries that play both sides and have no allegiance, added to the mix. I mean, we all know for a fact that if you summon and work with Devils you would never never summon and work with the mercenaries devils use to fight with them, right?
And again, who is this long-time fan, needing a lesson in basic world-building, who cannot accept that people touched by the Lower PLanes can come from this area of the map where people worship and make deals with the lower planes, and is ruled by a half-demon?
We are talking about the world building. It is all tell. You can't "show" in world-building. So this doesn't matter. They said it before, they can say it again.
And that is entirely possible to do. As mentioned, you don't exactly need to sit down, hold someone's hand and explain "so, in the 80's, we did things differently, so this is what it used to say, then in 2000 we did this, and now, we are changing it again, okay? And we are changing it to this" Especially when the person has never played or read any old Greyhawk material.
They can update it trivially as part of the lesson in world-building. It can be done. It isn't some sisyphean task that WotC is doomed to fail. Most of the changes aren't even actually changes, and are only being proposed to make pendantic fans of the 80's who hated what was done in the 2000's happy. ANd they aren't going to be happy regardless.