system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The end of the Lord of the Rings

Where are the elves, Gandalf, and Bilbo going? Why does Frodo have to go? Thanks.
gpt
The story takes place at a crossroad where the age of elves and magic is dying out and the age of man is emerging.  Lothlórien and Rivendale are two of the last bastions of elven magic in the known world, overall it has been waning and dying out as elves leave.   With the rise of the kingdoms of man the remaining elves led by Galadriel and Elrond decide to pack it in and migrate to Valinor, or the "Undying Lands" and leave middle-earth to to man.

Frodo is so much in agony due to being wounded by the Nazgul, he is also just totally spent by carrying the ring all that time.  The elves allow him to come with them.  His friends are distraught over this but in many ways understand.