Why are they called "worlds", and not "towns"?

Could go even more into what a "world" is.

For example the "Rock Music" world. (Fat bottom girls make the rocking world go round) :D The "animal world". The "Arab world", the "western world", the "ancient world", the "vegan world", the "Sims Community" world. ;)

Or if in love, someone could be the 'world' to you.

Many examples. "World" basically means something that is percieved by someone and/or a group.

In "Lord of the Rings", the Hobbits world was their Shire.