Simply put: Because Switzerland did not have that much strategic value for Germany, and because it is incredibly difficult to invade. In addition, Nazi Germany had a financial motive to leave Switzerland alone: they sold a lot of gold to Switzerland.
On a map of Europe it is seen that Switzerland is enclosed between Germany, Austria, Italy and France.
Italy was already an ally of Germany and Austria was made in March 1938 part of Germany. Therefore, control over Switzerland to conquer these two areas was not necessary.
Switzerland is also surrounded by high mountains, and in three days time managed to mobilize about 850,000 soldiers when the war broke out in 1939.This, combined with a clever defensive tactic, makes that an attack on Switzerland would cost a lot of effort. The Swiss had thought that, should the country be attacked, the army would keep itself in well defended and favoured forts in the mountains. In this way, it would be very difficult to get them out of the mountains with violence, so it would be an attacker to take a lot of time, manpower and equipment to conquer Switzerland.
In order to attack France, control over Switzerland was not really necessary: there was already one (as history proves) an excellent plan to attack France via the Netherlands and Belgium.From Belgium It is also much less far to Paris than from Switzerland.
The Nazis described Switzerland after the victory in France as “a pimst in the middle of Europe”, a state that has no right to exist, and populated by “the most vile and miserable people, the primeal enemies of the new Germany”.Himmler’s plan was to purify Switzerland racially. As of June 1940, plans were made to invade together with Italy in Operation Tannenbaum-Wikipedia.About 11 German divies and 15 Italian divisions with 300 -500 000 were reserved for the raid. Eventually, Hitler never put the plans into execution. Politically, there was not much to take advantage of in the conquest of Switzerland. The raid the following year in Russia was more important.
It was knarsetandend.Hitler hated the Swiss and Switzerland. It never became clear why he did that. During the Blitzkrieg in the west there was a plan Tannenbaum (Denneboom), which was the invasion and occupation of Switzerland: from France, once that country was fully occupied, a two-pronged attack on the Swiss would take place-one From France and the other from Germany.
Given the geography, the fact that the Swiss Nijver had collaborated with the Germans (VNL on the persecution of the Jews in the late 30s-the fact that Jews had to have a large “J” in their passports was a Swiss idea), but mainly because the Nazis Had found that the Swiss were willing to cooperate and had a potproof bank secret, the Swiss were left alone.They became the bankers of Nazi Germany: Untold amounts of gold, money, securities and also art was stored in Switzerland.
Switzerland, although Hitler hated it, proved to be more useful as a lucky and banker, than as an enemy.The Tannenbaum plan disappeared in the refrigerator to never get out of it.
Anyway they had to park their money somewhere for when it went wrong?