First, the most important reason is that Switzerland and Germany share the same language and species. It is a small country separated from the country and the nation. It has always been a potential ally of Germany. It made great contributions to Germany in the war and invested heavily in German top leaders such as Green, so it was not attacked. That's all that matters.
Second, Switzerland is a small mountainous country with no strategic resources, no transportation hub and no strong military industry. On this basis, the occupation of Switzerland has no substantial help for the improvement of German military strength.
Third, it is more important to leave Switzerland as a buffer, negotiation, information exchange and material exchange place with belligerents. Just like leaving Hong Kong after the founding of the People's Republic of China.
As for saying that all people in Switzerland are soldiers, this is a joke. Many countries fought bloody battles against German aggression, especially Yugoslavia. The point is that Germany will not invade again.