Not OP, but presumably Switzerland is "in the EU" the same way Hawai'i is in the ocean. It's objectively above sea level, and not literally in the ocean. But when you're surrounded by ocean to that extent, it can have a large impact on the way life is lived.
When one entity has so much leverage over another it compromises the sovereignty of the other.
Also it's a 'gray area' -- Switzerland belongs to many EU institutions like Schengen and EEA without being in the EU proper. Using Euros would also be common in parts of Switzerland.