Could it be that we in the UK don't get it because we actually have an awful lot of real history on our doorsteps? So we don't need to pretend too much?

What a load of shit. No one "has more history" than someone else, much less more "real" history.

And I guess they do cos-play in Japan because they don't have enough of real anime characters around them, unlike in Argentina. And they don't have Halloween in Uzbekistan because there are lots of real ghosts and goblins floating around there. And why Ren-Faires are most popular in the state of Hawai'i, where the natives have only started having real history since 1959, and before that people never dressed up.