I guess the big problem with releasing big adventure books or APs in less-D&D-standard worlds is precisely that they're not FR and therefore less adaptable.
I could run CoS in Greyhawk or Exandria perfectly happily, and Eberron without too much difficulty. Princes of the Apocalypse, Ghosts of Saltmarsh, Out of the Abyss are all pretty adaptable too. Change the names of the gods around, find an appropriate spot in the world for the action to happen, reskin a few NPCs as Warforged or whatever as appropriate and you're golden. Some of the big adventures (the Tiamat series) can have some hiccups due to the nature of Eberron dragons, for instance, but on the whole it can work.
What you don't get by doing this is actual setting feel though. If you're writing an eberron epic campaign from scratch, you're going to have stuff like the lightning rail, dragonmarks, warforged, artificers, etc prominent. Have the cool bits of the campaign front and centre. A converted FR adventure just isn't going to have any of this, without a fair bit of additional work, adding new plotlines, rewriting encounters, etc etc. But if you're doing that much work, why are you running a pre-written campaign anyway? The whole point it to cut out some of your prep time.
Conversely, if I write that epic Eberron (or Dark Sun, or Spelljammer...) AP, it's definitely going to include all the cool setting-specific stuff. But by it's nature, that makes it less adaptable. If my hardcover Dark Sun megaadventure is stuffed full of psionics and defiling magic and sorcerer-kings and widespread slavery - it could probably be a great DS campaign, but you'd NEVER hammer that square peg back into a FR- or GH or DL-shaped round hole. Which is why it won't happen. You can only really sell a DS adventure to DS players (though I guess Avernus is a quasi-planescape adventure and you could do a similarly structured adventure with Spelljammer) and with the small number of books getting released per year, I can't see WotC willingly making a product that's appeal to only a relatively nice audience.
(Hell, for really out-there worlds like Dark Sun, any adventure conversion is difficult either way. I started putting together a DS port of Rise of the Runelords once, and basically every encounter, most creatures and NPCs, and most adventure locations needed redesign. Goblins, aasimar, barghests, cults of evil gods, timbermills - all utterly non-DS and all front and centre from the very first book in the 6-book campaign. And it only got more difficult as it went. Isolated farms amid waving rows of grain? Scarecrows? Sea monsters in the town dam? Even the character motivations are messed up, so many bad guys worshipping evil gods. You end up throwing out more than you use.)