Thing is, they already made those changes to Greyhawk in 2019, and the blowback was...not significant. Co siderimg it produced one of the best selling 5E books.The fantasy that kids are consuming today tends not to be medieval and it tends to have a bit of cutesy weird built in. Imagine the uproar from grogs if they cutsey-weirdified Greyhawk to make it palatable to The Kids.
That's what i mean by baggage and why i think something completely new works better as an example and teaching setting for 5E 2024. They don't have to hammer any square pegs into round holes, don't have to erase any canon, and don't have to pretend perform convoluted retcons to explain why dwarves can be wizards and where dragonborn came from (or whatever).
it is true that you can do the teaching part with some location in Greyhawk or with Nentir Vale or a new setting equally effectively. but the benefits of being fresh and unencumbered and built for the audience far outweigh the perceived value of the Greyhawk or Nentir Vale brands. Obviously IMO and YMMV and all that. I just have not heard a compelling argument that suggests you can make Greyhawk current and relevant more easily and effectively than doing something new.