People didn’t used to do this. Guns at school, guns in pickup truck gunracks. What changed? What is different now? A Godless society. Kids drugged for “ADHD”, perhaps all it took was for Columbine to “break the ice”, and now its a thing. Something happened. People didn’t behave like this a few decades ago.
Lots of things happened. The population became more dense and yet more isolated from each other. Households where mom stayed at home while dad worked became all but extinct. Businesses learned that they could maximize profits by creating products that had the side effect of shortening attention spans and increasing impulsivity. And not to blame guns, but there are simply hundreds of millions more of them around than there were, say, 40 years ago.