IMO it's a combination of terrible social safety net (typical, and not specific to the US) and obsession with firearms (that other firearm-friendly countries don't have).
Owning a gun in the US is a political statement about the second amendment, which while laudable on paper is clearly a failure since none of the collective gun ownership actually does anything to keep the government/law enforcement honest (I'd argue it makes it worse as every cop is more on the edge that they would be otherwise).
This leads many people to obtain guns that otherwise have no time/desire to learn & practice responsible firearm ownership and enjoy their firearm safely without harming anyone. The firearm then mostly collects dust until it gets misused in a freak accident or falls into the wrong hands.
