I think Social Media plays a huge part in this as well. Back in the day if you were bullied at school you could go home, play with your friends on the block and shrug off the crap you deal with at school. But now every kid is hooked 24/7 into their iphone where they can be bullied every minute of the day. Even worse, kids get addicted to the dopamine hit from getting views and likes and the jealousy in their face of classmates having more popular accounts. Combine that with a modern culture that practically worships Nihilism and you have a kid that thinks their phone is reality and cant escape the bullying, has no real purpose in life beyond that and knows there is one thing he can do that will 100% get him more attention than anyone on TikTok.
We have always had guns in America but if you look at the rise of Social Media in the USA it closely follows the trends of mass shootings.