They're different communities with the same name, because community names don't have to be unique between different instances. I get that subscribing to two different communities with the same theme is annoying when you could save time and subscribe to one, but having backup communities is a blessing when the instance shuts down or mods start power tripping. A "multireddit" feature that can combine multiple communities into one subscription feed would keep subscribing convenient without forcing only one community to exist per topic.