I agree with you on this. The reason why I have never really bothered with high-level adventuring is because I'm of the opinion that high-level adventurers should be moving on to bigger-scaled adventures. Going plane-hopping being the most obvious direction. But if you aren't having the PCs do that, then high-level adventuring gains you nothing. For my money, having 16th level PCs running around a duchy solving the same sorts of issues they did at 6th level is a pointless endeavor. Yeah, they all get to use their brand-spanking new and pretty game mechanics... but the story is no different. And that to me is a grand waste of time and energy.
I saw this especially true in a number of the 4E so-called 'Epic Tier' adventures you could get through D&D Insider. We're talking adventures for PCs in levels 20-25 that are about solving run-of-the-mill problems, only that the monsters that get thrown at them have massive CRs. I just pulled up one of them randomly, 'Winter Of The Witch'... and this one sends Level 22 PCs back to the village of Winterhaven (the introductory village in 4E's first Level 1 adventure 'Keep On The Shadowfell') to deal with a fey witch who has made the Nentir Vale really cold. And the party's expected to go traipsing across the Vale to find some magic items, destroy a bunch of demons, and then deal with this fey and solve the ice problem. An adventure that players could easily have done back at something like 5th level (if the CRs were just lowered).
So yeah... they gave us some 'Epic Tier' adventures for us... but really, what is so epic about them? What's the point? The levels might be higher, but the actual adventures are no different! At this point if anyone needed a high-level adventure they could just take another adventure written for 7th and 8th level PCs and just swap out the monsters for more powerful versions, if the stories are going to all be the same. And if that's the case... then needing WotC to do it for us is a massive of waste of time. We can just make these things ourselves.
One could easily imagine those sorts of quests working if say, the Witch of Winter had transformed the entire Nentir Vale into a Domain of Dread (or a Winter Court/Gloaming Court Fey Domain of Delight; I don't recall the thematic underpinnings of the adventure and it's not particularly important). You'd then have to deal with the consequences of being trapped by the Mists of Ravenloft, or time and space dilation messing with everything as you go around killing those demons, and it would matter to you because you started your adventures here and presumably the NPCs now caught in the STORY of the Domain and forced to carry out the actions of the whims of the Domain's Dark Lord/Archfey until the spell is broken.
There are ways to make it work, but if it's the SAME reality rules, then yeah, it feels like taking a Companions (Fighter's Guild) quest to clear out a bandit hole that you might have taken way back at the start of Skyrim, but since the players are higher level now, the bandits are also now lv 50 Bandit LORDs instead of lv 5 Bandits… It's number scaling without meaningful consequence changes. It's tougher so that you can't make quick work of it but it's rote and repetitive.
Mind you, that's also old school gaming to some extent -- you might spend your entire campaign exploring Castle Greyhawk, just with more difficult challenges at the end. Or an entirely dungeon campaign set in Moria might fight goblins and orcs for the first 10 levels, then have to take on the Watcher of the Waters as a major tier-ending boss fight, before eventually fighting hordes of Orcs later on and then encountering the Balrog at the very end and highest tier of the game. Fighting a more powerful enemy can be made interesting and be considered epic -- the Balrog's lair actions, the way the Balrog literally causes the mines to burn and boil, the bridges and stairs collapsing and now what was once a mine is now an MC Escher painting but falling on top of you and from below your feet -- that can all be considered a major consequential change despite being in the "same" location the entire campaign. So "now you fight demons" in the Nentir Vale could be considerably epic if demons are all epic tier threats with major world-transforming elements and consequences. Of course, my recollection is that that adventure didn't build all of that into fighting demons, but instead they were just stat blocks to be fought.
There were plenty of other articles you could combine with it to mod out your campaign there to make it more epic, but that takes work and what DMs want with published adventures is something ready-made that is appropriate for the tier of the game.
I think the biggest difference now though is that WotC has a LOT less pressure to churn out "content" for the player base (including content for DMs) because of the DM's Guild. A big part of why 2017 saw us drop from 2 Adventure Paths per year to 1 (and 1 AL season alongside it, though starting in 2018 when they realised that the previous year's anthology book wasn't actually an adventure path), was because they could now trust there to be enough high quality content on the 'Guild to fill in the gaps (and even now directed you to semi-officially-sanctioned tie-in content via the Guild Adepts program, appropriately starting with 2017's Tomb of Annihilation). Guild Adept program is dead now, but I understand more so because they don't need to put that effort in given that the community has such great content they churn out as well and creating that artificial dichotomy between Guild Adept content and Guild content elevated some content to high seller status over equally good or even better content that just didn't have that gold stamp of approval from WotC. In any case, the Guild also has Epic Tier handbooks and all sorts of other modular elements that WotC sometimes has mimicked with
Core Rules revisions and/or
Rules Expansion content. I'm especially looking at how many of the
Xanathar's Lost Notes to Everything Else subclasses have been mimicked by
Tasha's Cauldron of Everything and other subclasses published in official WotC books.
WotC doesn't NEED to give us those epic tier content as long as they have good enough guidance in the 2024
Core Rules for DMs on the Guild to make us that content and make it feel appropriately epic.
D&D Insider was indeed subcontracting out writing to DMs from the D&D community, but it had a lot more integration with WotC than the DM's Guild does -- they at least had to look over and review and approve everything that showed up there, even if the writers weren't on staff (though some were). That's a LOT of time and effort for WotC when they can just get their paycut from licensing fees from us publishing via the DM's Guild now -- yes, of course we could publish via other licenses and use DriveThuRPG's non-licensed storefront or our our storefronts or else via Patreon, and I know that game creators and publishers like
@Morrus have had great success in that way. I LOVE
En5ider, for example, and I know that others here love
Level Up 5e (for me,
En5ider is the missing piece that
Dragon+ failed to deliver on, though I appreciate
D&D Beyond's more recent steady stream of articles that are
Dragon-esque, even though the vast majority aren't providing direct new mechanics to play with -- I have a feeling part of that arose from the purchase of the site by WotC).
What I really want WotC to do is provide us with
Core Rules Epic Boons, front and center as part of the PHB, and a chapter or significant chunk of a chapter in the DMG that covers how to write and run higher tier gameplay. I also would like to see the return of the 2-book Adventure Path modules like with
Tyranny of Dragons and
Waterdeep, though I wouldn't be surprised if they brought it back in 2018 just to try it out again and decided "nope it really does still cut into our sales by splitting the buyer-base between the two books." But if not 2 books, provide AP books that carry us to those higher tiers, not cut out at 10th or 15th. If that means a chunkier book, then by all means. I don't mind if a Campaign Setting comes with a shorter adventure --
Spelljammer and
Planescape are both trying to be an AP, a Campaign Setting Gazetteer, a PHB expansion for the setting, and a MM expansion for the setting. And I don't expect the new Phandelver book to get to 20th Level because it's expanding on the Starter Set adventure and intended to build straight off of that (if it doesn't include that adventure republished inside of it, outright). But I do want to see at least some APs have that high tier content, especially if they're pitting us against the threat of Tiamat or the Princes of Elemental Evil or the Demon Princes or the Archdukes of Hell… it's okay if the adventure for the most part considers these threats out of our league, but I want at least a chapter or two in the back of the book on continuing it to Epic Tiers and how to appropriately challenge the players on taking on the BBEGs rather than just having them as a threat too powerful to ever realistically challenge. It could even be something like the
Domains of Delight pdf released alongside
The Wilds Beyond the Witchlight -- something that realistically should have been part of the book but was given to us/sold as a separate digital release to expand on the book. Could be like the
Monstrous Compendiums that are released to
D&D Beyond -- but instead be something like "Continuing the Adventure."
I don't need D&D to have an official Epic Level Handbook -- D&D Beyond already has a number of high quality options in that front. But I do want WotC to consider it as part of their APs and give DMs Guidance on it. This is the best chance they have since Perkins is getting all the time he could feasibly need to focus nigh-100% on a revised DMG that greatly improves the guidance to DMs.