Not everyone can what?
Update a setting? That requires zero work. You can use any of WotC's published adventures in Golarion effortlessly.
Update an adventure path? Yeah, that's slightly harder. But it just requires some knowledge of building encounters, and is less time consuming that doing a homebrew game. If you don't have the skill in the edition and in adventure design for than, then you probably should be sticking to the prepublished stuff anyway. But if you never design an encounter, if you never try converting an older edition adventure, you'll never learn those skills.
I'll also be "that guy". If it's a "time thing" and you simply do not have the time to plan a homebrew adventure or even convert 5-6 encounters from Pathfinder to 5e then maybe, just maybe, you shouldn't be GMing a game. If you're that short of time, maybe you need to pass the reins to someone else in the group and just play.
If people don't have the time to sort through the existing 3rd Party campaign settings, WotC adding another option to the mix is NOT going to help.
If WotC continually isn't releasing products you want
find another game. Seriously. If a band stops releasing albums I like to listen to, I don't keep buying just their music. I find other bands. There's a tonn of great 3rd Party stuff out there.
I recommend starting with Kobold Press, who have a campaign setting and adventures. Or check out Primeval Thule.
Or go for a D&D-esque game like
Adventures in Middle Earth or
Amethyst: Quintessence. Perhaps
13th Age or
Shadow of the Demon Lord.
They tease because pople
ask. They're answering the question. People keep asking about other settings and so they respond. Because if WotC doesn't, people WILL complain about them ignoring other settings. Because that's what happened. WotC teases because they got tired of people whining about how they were ignoring other settings.
This is a catch-22 situation for Wizards staff, because people are going to complain regardless.
Yes, they have plans. But they've also planned the line for a decade in advance and are focusing heavily on the basics. They're not going to blast the market with a decade of products over two years, because that kills the game line. And they're not going to go to Dark Sun before getting the basics done in the Realms.
I sympathise that you're not getting products you like. But WotC is a business and is under no obligation to release products just to make people happy. They haven't even released a real campaign setting for the Realms, why would they do one for another setting?
And they know the majority of players don't even use their existing setting of the Realms. Why would they add a second setting that an even smaller percentage will use?
The published adventures work and sell because they're easy enough for gamers running homebrew worlds to fairly easily convert to their homebrew settings.
They did sidebars in
Princes of the Apocalypse for converting the adventure. If that had been well received, I think they would have kept doing that in future books. But, honestly, that was a couple pages that could be better spent doing anything else, and getting the author to write that really requires a lot of setting lore of all settings. Generally, fans of the setting will know it better and be able to convert adventures on their own.
If you're having problems converting adventures, maybe start a thread that will help you convert one.
I've thought a "guide to other settings" product would have been cool and have been hyping that for years. But they're only doing one accessory every year, so I can see why that's a later release.
Even then, it's not like Greyhawk or Mystara or Planescape really need much content to be updated. Dragonlance just needs moon magic, Spelljammer just needs the rules for spelljamming and ships, Eberron needs five races and dragonmarks. That's all of a dozen pages. And it's hardly essential. You don't
need the fancy Eberron races to play in Eberron. The big one would be Dark Sun that has several new races as well as a whole book of new monsters. That one is likely beyond the scope of a single 5e product.
The catch is, what's
needed to convert an adventure to another setting?? (Excluding Spelljammer, Planescape, and Dark Sun)
You don't need any new crunch for that. You just need a location and to change some proper names. You need the lore of the setting and the ability to swap out, say, Waterdeep for Greyhawk or Palanthas and details on those locations. AND ALL THAT CONTENT IS ALREADY AVAILABLE.
If you wanted to change the upcoming
Dragon Heist adventure to Dragonlance, you'd probably just need
this book and maybe a
campaign setting or
two. And even odds a Dragonlance fan has those books on their shelf already.
WotC can
only offer them content they already have.
That's an older gamer problem.
The vast, vast majority of 5e gamers are not bored with generic fantasy, either being new to D&D and not jaded with the tropes, or being experienced and knowing there's other RPGs out there for different styles of fantasy and either sticking with D&D because they want a generic pseudo-medieval fantasy game or being skilled enough to add non-generic elements.
The big advantage with generic locations is they're
easier to make less generic and add into your homebrew non-generic world. It's easy to add towers and craziness into Waterdeep, making it Sharn or Sigil, or a homebrew city built atop the shell of a giant turtle. But if you have an adventure set in Sharn, it's going to be that much harder to set it any other location. A Sharn adventure is pretty much only good for Sharn. Which makes the product
significantly less useful.
That's the reason WotC is using the Realms. It's the baseline flavour for people who don't have the time to invent their own world, to save them the time of inventing a whole bunch of proper nouns, but generic enough it can fit into most people's homebrew world without a lot of work. A non-generic adventure is just going to make more work for a solid majority of their audience.
If you want something beyond the baseline, you're just going to have to look farther away from the big name company publishing safe books designed for mainstream appeal.