Your supply side argument fails when EVERY Swiss household is likely to have a full mil-spec firearm inside it...unlike the US. This means the per household chance of coming in contact with a firearm is HIGHER than in the US. While the US may have 90 firearms per 100 people, many (if not most) of firearms owners have more than 1 gun. I, for example, own 3. I have friends whose collections number in the 100s. The likelihood of there being another house on my block with a firearm is statistically low....lower than the likelihood of them having a dog over 40lbs.
The Culture of the Swiss is not one where firearms are seen as for personal use...hence a lower issue with them. Also, the Swiss' penchant for being the "neutral" nation has caused outsiders who may agitate in some nations to leave the Swiss alone...so they can use Switzerland as the go between (or safe haven for their funds). If they caused issues in Switzerland, then that government may actually take a position on their activities and so become persona non grata.
It is a cultural issue, not a supply and demand issue. If there were a cultural want of firearms, there are plenty of people to supply them. See many parts of Africa, Northern Ireland, etc for examples of where these is a demand, there will be a supply.
While in the military, I discovered while deployed in various places around the world, weapons are cheap and plentiful if you want them. Hell, in some countries, their military will take you to their armory and let you pick out what you want for the right price! And the right price is a LOT lower than you would think!