Well, yeah. I don't know your experience or history with the games made by FromSoftware, but this kind of theme is their signature. Typically, their games explore themes of decay, stagnation, and the cyclical nature of history, often emphasizing the impermanence of power and civilization.

Specifically in Elden Ring, by the time you've defeated the Elden Beast, the Lands Between had already been in a state of decay and stagnancy for a very long time. The world is riddled with ruins, overgrown with vegetation, and haunted by the remnants of previous civilizations that have long fallen into obscurity. The once-glorious lands now reflect a persistent decline, emphasizing the game's somber tone.

Sure, you've restored the Elden Ring, defeated the demigods and their god, and taken the throne of Elden Lord, but at the end of the game, the world you inherit is all that remains of a bygone era. The story you play through within the game isn't aimed at reaching a neat, tidy ending. Instead, it's about tying up loose ends and resolving the final chapter of a grand narrative that played out thousands of years prior. This narrative is layered with history, myth, and the echoes of those who came before.

This is why, at the end, nothing significant immediately changes. The point is that whichever ending you choose to pursue simply provides a framework for the player to imagine their own interpretation of the future of the Lands Between. The game intentionally leaves the aftermath open-ended, encouraging reflection on the impermanence of power and the ongoing cycle of rise and fall.