I would not say they've never been involved in a conflict. One of the more well-known cases occurred in 58 BCE when the Helvetii tribes attempted to conquer neighboring territory. A Roman commander ended up moving his forces into the Rhone valley to block them, following up at Bibracte where he smashed most of their forces. The Roman commander's name was Julius Caesar, and he ended up striking a deal with them where he offered protection and shipments of grain to alleviate the threat of famine they faced in their territory, and in exchange they would send him tribute and guard the border against Germanic tribes.

The deal worked out pretty well for them, as it turned out. The actual name of the country commonly called Switzerland is the Helvetian Confederation.

Why send your people off to fight and die in foreign lands when your homeland is one of the most defensible territories on the planet and you can just stay neutral most of the time?