why couldnt frodo return to the shyre ?

I had read all of the books by the time I was in fifth grade and a lot of the story still sticks with me toda.

Anyway, Bilbo in the end heads off with the elves to their land to the west, which I can suppose is another dimension, anyway they are like several thousands of years old, and the message is that Bilbo now only feels comfortable with people of such experience.

I’m sure that that was a commond feeling after WWI for many Europeans.