Although Swiss Industry supplied the German war effort and the country supplied a secure rail link between Germany and Italy, the Allies left Switzerland untouched, even in late 1944 for the same reason that Germany and Italy did not invade in 1940.
Switzerland was where everyone did business.
Although Germany operated under a number of political trade sanctions from 1938 onwards, business carried on as usual with many countries. The USA happily did business with the Reich openly until December 1941 and even afterwards through front companies as did many other countries. Before January and May 1940 most front companies were based in Denmark and Holland respectively before consolidating in Switzerland.
The German Mark was not a convertible currency during the National Socialist period and pre-war trade was conducted via barter or the use of gold or hard currency earned through exports. Barter deals were “monetised” in Switzerland After WW2 started the only hard currencies generally acceptable were the Pound Sterling, the French Franc, the US and Canadian Dollar and the Swiss Franc and after the fall of France the French Franc became worthless and the USA refused to accept Sterling—demanding that Britain pay for all supplies in gold bullion, US dollars or Swiss Francs.
The world of finance, as we have all re-discovered since 2008, has absolutely no morals whatsoever and despite the war, business continued. British, German, French, American, Swiss and other bankers would sit down every month in Geneva throughout WW2 and discuss pre-war debts, transactions and their settlement. Significantly “enemy assets” that had been seized or frozen in warring countries, still earned dividends or interest and these were accounted for and credited ( although not paid over) under the supervision of Swiss banks. (General Motors earned a fortune on paper from Opel tank production and WW2 was very profitable for Coca Cola). If German companies wanted to buy, say, Wolfram, from Portugal or canned fish from Turkey they paid in hard currency (or stolen gold) via Swiss banks. Sterling that came into the hands of German banks or US Dollars after December 1941 could hardly be credited in London or New York, so they were naturally exchanged for Swiss Francs in Zurich.
Switzerland was of more use to everyone as a compliant neutral whatever way the wind blew.