Belgian neutrality was only based on a British guarantee, and nothing more. The Germans quite literally referred to is as a "piece of paper". Swiss neutrality, on the other hand, is based on centuries of independence from expansionist powers on account of their location in the mountains making an ideal defensive position. Because of that, ALL major financial interests in the 20th century kept their money safe there. Even still, Hitler had initiated
plans for an invasion but never gave the green light. While there's no definitive evidence, many historians agree that Hitler most likely recognized the tactical nightmare it would be, especially considering the Wermacht's reliance on blitzkrieg and need to quickly secure the western front.
Even today, the Swiss Guard provides personal protection for the Pope.