The numbers. There are millions upon millions of guns out there among the people, now. Many of them are not being properly locked up, and are being given away or sold to others with no record of the change of hands or background checks at all. Also, the guns are now mostly very fast repeaters that can carry a lot of rounds in a clip.
But most of all they are now a fetish. They represent self-reliance and self-determination and strength to a lot of people that have had these taken away from them by an economic system that's rigged against them, and rigged to enslave and control them. The more they feel their autonomy slipping away from them in this culture of systematized greed, the more they desire some way to gain that sense of autonomy back. And guns are our culture's most notorious symbol of that self-reliance and autonomy. So now millions of Americans are obsessed with them. With having them and showing everyone else that they have them. And especially with thinking that having them makes them powerful and respected, again. Men, again.