To expand on this a bit (okay, a lot). If your view of "lore" is that it is primarily
the story of the worlds of the D&D cosmology (i.e. metaplot), then there is definitely a thread running from 1e-3e that was broken for 4e and 5e. However, if your view of lore is that it is more the backstories of individual monsters, places and items, then you probably didn't experience quite as much of a disconnect across editions.
The approach to D&D continuity has varied a fair amount across editions.
1st Edition
When the
Monster Manual was published there wasn't exactly a lot of existing Basic D&D to be consistent with, but it is worth noting that the B/X and BECMI line of D&D products ran all the way through 1e with no effort made to keep any form of continuity between the lines. Events occurring in one line had no impact on the other, the cosmology and hierarchy of divine beings/immortals was very different. Monsters with the same name had different abilities. The D&D brand was quite happy to have a biversal approach to lore throughout this period with seeming little complaint from customers. Only in the 2e era was the Basic D&D line finally merged into the main D&D line as the world of Mystara.
2nd Edition
This is the edition of the rules that was the most respectful of past lore, typically treating all 1e content as canon, and expanding the cosmology to explain the existence of myriad campaigns worlds, even eventually incorporating Basic D&D/Mystara. In-world reasons were provided for most lore changes resulting from mechanical differences between 1e and 2e. The 2e approach to continuity was additive, avoiding new lore that contradicted existing lore. When 2e did contradict past lore, it was almost always accidentally, and simply because there was so much lore to keep track of.
3rd Edition
This was the first edition that wasn't shy to drop lore that didn't work well mechanically, or which needed streamlining. Overall, 3e tended to be mostly respectful of lore from past core books, fairly respectful to lore from past adventures and supplements and occasionally respectful to lore from D&D magazines and other sources. For 3e, you were less likely to get an in-game reason for changed lore; the approach was typically to pretend that things had simply always been that way. ("Yes, galeb duhr have always had four limbs, why do you ask?") Campaign setting material tended to be compilations, updates and expansions of older sources with a gradual progression of world timelines.
4th Edition
This was the edition by far the least respectful of past lore, entirely by design. Not only did the rules system get a significant overhaul, but the cosmology, origins of the world, and backstories of many creatures were rewritten. This edition took liberties with settings too. The Forgotten Realms had a massive timeline jump and another cataclysmic event. Dark Sun was rebooted back to the beginning of its original timeline. Only Eberron escaped significant change, with 4e keeping the timeline where it was in 3e.
5th Edition
The current version of D&D is respectful of past lore, but ready (sometimes even eager) to ditch anything that gets in the way of modern design goals. 5e draws heavily on all previous editions, but does not further develop the existing timelines of any settings (except vaguely the Forgotten Realms), preferring to reboot (Ravenloft), reset (Planescape, Greyhawk) or selectively reuse (Dragonlance, Spelljammer) settings as seems appropriate to make them accessible to newer D&D players. 5e has probably made the most changes to monster lore
within an edition, something which didn't start with the 2024 rules, but goes back to at least
Monsters of the Multiverse.
This evolving approach to D&D continuity is complex enough that I have no trouble understanding several seemingly conflicting opinions. I get
@Micah Sweet's distress that the story of the D&D cosmology is no longer being told. I understand
@the Jester's disdain for mid-edition tweaks to monster classifications. I can also see why many people don't see any problem with how 5e treats D&D's rich history of lore, or at least don't agree that 5e is less respectful of lore than past editions. Those views are shaped by different perspectives of what D&D lore is and how immutable it should be.
