> if someone uses a gun to shoot down someone, why is the company providing the gun not held accountable here?

The gun company will claim they sold for self defense or just for a hobbyist's collection - They'll claim that the gun owner used it for something else is not their responsibility. Same for any or product that can be used to kill someone with.

Let's not forget sports, which is a huge segment of the gun-owning public - trap, skeet, biathlon, PRS, USPSA/IPSC, High Power/CMP, etc.