They caught on because they were first, not because they were good. Greyhawk was a terrible pile of steaming garbage compared to modern settings - but that’s because a huge amount has been learned about building worlds for D&D since it was published.
And yet -- it works well in the 2024 Dungeon Master's Guide as a limited-scope setting gazetteer as opposed to justifying two whole books to cover just the Eurofantasy pastiche part of the setting (i.e., Forgotten Realms' new books).
I still think that if not for the 50th anniversary, they could have just as easily gotten away with using the Nentir Vale and surrounding areas (Mithralfast, Trollhaunt Warrens, Vor Rukoth, Chaos Scar, etc). But 50th anniversary nostalgia glasses are powerful, and they also wanted a setting that would prop up the Greyhawk pantheon propped up by Planescape, rather than one that would want to center the Dawn War Pantheon from the 2014 DMG & Explorer's Guide to Wildemount.
I still have hopes for a Nentir Vale Gazetteer book that clocks into the 2024 Revised 5e rueleset. I think the main thing going against it is that it was pastiche of FR, Greyhawk, Eberron, Dragonlance, and Ravenloft elements, so as to center in all the important modules of D&D history, but with Greyhawk present not in the 2024 rules, they can just put places like Sunless Citadel or Tomb of Horrors or Temple of Elemental Evil back in their home setting (and in fact, already did so with anthologies like
Tales From the Yawning Portal or
Quests from the Infinite Staircase). That said, they also tried to squeeze those same modules into Toril in AL seasons such as Elemental Evil, Chult, and most notably when they made a season around
TFtYP and put follow-up adventures to several Greyhawk-set epics but the follow-ups are in Faerûn for some reason). That would suggest that it's okay that these adventure destinations have echoes on multiple worlds. Elemental Evil and Chult AL Seasons even said as much that they do. So that opens the door for 4E's premiere campaign setting to get some love at SOME POINT.
I still expect
Dark Sun and another
Critical Role book, and another
Planescape book, all well before then.
Dark Sun is a given, but
Planescape feels like the space they can expand in the most while being useful for home games due to DMG-enforced shared assumptions of the Great Wheel. We got a heavy focus on Sigil and the Outlands, but a true
Manual of the Planes diving deeper into the Inner and Outer Planes, give us Ardlings and Glitchlings and throw Plasmoids in thoo to rempresent Limbo, and now we're cooking with spam!
Critical Role getting another official book is almost a given – especially since they've moved onto a new world in Campaign 4 (Aramán). Marquet was included in
Call from the Neverdeep and Tal'Dorei's remastered 3rd-party settingbook has been released on D&D Beyond, so whether they'd do another EXANDRIA book is up for question. I think you could do an Exandria-wide Gazetteer updating material from Explorers of Wildemount like the Pallid Elves, Draconbloods, Ravenites, Graviturges, Chronurgists, Echo Knights, etc, and updating non-EoW player material like the Cobalt Soul Warrior, the Gunslinger, and the Blood Hunter. Such a book would not be able to go as deep into Wildemount or Tal'Dorei as their respective books do, but it would let players get a sense of the entirety of Exandria now that CR has moved onto new worlds.