system
Given the following post, respond as if you're commenting on Reddit:
human
[LotR] If Arda is Earth, what happened to the other races (dwarves, hobbits, goblins, etc.) in the Fourth Age? Why aren't they here now?
gpt
The Elves largely left for the undying lands, the rest have successfully remained invisible or simply died (and thus returned to the Undying Lands via the Halls of Mandos).

The Hobbits have ways of remaining unseen by the big people if they wish to remain unseen, so they probably have a small hidden community somewhere in Europe.

Goblins/Orcs have either fled into the depths of the earth or simply died out.  Without a strong leader in the 4th Age they wouldn't be able to stand up against the nations of men in any meaningful way.

The Dwarves were already on a slow decline due to deaths and low birthrates.  They are either extinct or have a small, tight-knit community somewhere underground away from human eyes.

The Ents have most likely gone tree-ish to large degrees or been cut down due to large scale deforestation.