It’s weird because Switzerland is one of the most armed countries in Europe, as in they have firearms but barely any shootings of any kind (so you don’t often hear news equivalent to a guy shooting students in a classroom or killing people at a shopping mall over there). Part of it has to do with the draft (most people who purchase firearms have a form of training, as they learnt how to properly handle them during military service).
Because nearly all of those arms are under lock and key. They don’t exist for fun shooting. They are federal property which is stored in the homes of reservists in case they are called in. Like they have their uniform and other items for their countries defence at home for this event. And people don’t have the ammunition for it, which would be supplied at the assembly locations when push comes to shove.