It is due to the illegality, legitimacy of the product (too risky and scam-rampant), and also, affording it is a bit of a problem. With my firearm, it only cost me just a bit more than $200 (at that time) and also it is more accessible and legal where I live to own one. Therefore, while N might be more peaceful, it is not easily attainable compared to a firearm (which also has really high success rate when done correctly, albeit a very messy, gory corpse afterwards.). In some places a firearm would be bounds more difficult to get (all the licenses, good character references, long wait periods, additional screenings, etc.).