It would cut out a lot of the requests. While it might seem like adding the country to all the worlds is extra work, by only doing one country per world as and when requested, all you're really doing is deferring that work until someone asks for the add on. It makes more sense to have the same countries across all the worlds, and it's easier to standardise it now before there are too many extra worlds (imagine trying to compile a standardised list of all countries for 30+ sites, going through each one to check if there's a country you've missed).