yet believable, world like DeS, DS1 or Bloobdorne did
How exactly are these believable where ER wouldn't be? I'd say Souls games always exhibit a dream/myth/fairytale-like vibe akin to for example E.Y.E., Pathologic, Killer 7 etc. Sekiro is sort of an exeption but not all that much.
Lots of reasons. For once, DS1 cites lots of realms and lands beyond the game scope and gives you views hinting at those lands in the horizon...
...while Elden Ring lore hints at groups and realms and intrigue etc. within the very place the game is running, but then doesn't show how any of that could be plausibly the case, since there isn't even a population for that to happen. Except if the conflict is among dogs and mosquitoes.
The Kenneth Haite quest in Limgrave is the worst offender here: you find a noble on the road asking help to expels invaders from his castle, and citing he is the next in line for Limgrave throne, and that Godrick is an incompetent ruler.
I mean, wut? Where are this Haite fella serfs, court, farmers or their homes? Nowhere to be seen. What nobility is that which Godrick is ruling over? Nowhere to be seen. Where is the daily live of this realms, with commerce, diplomacy, sustenance, etc. hapenning? Nowhere to be seen. Do we see that court in the castle after the quest is accomplished? Nope, the place stays derelict.
The game world is simply too fragile in backing up what's claimed by the lore, in a way that past Souls games weren't (be by backing it up or smartly evading it altogether). All there is, is a theme-park of adventure for the player to romp through with little in the way of causal resonance to the lore that's presented in items and NPC dialogues.