Mostly, It's just people giving up. There are a few who want to push their agenda, ideology, etc. But for the most part, these teens that commit mass shootings are GIVING UP. If we limit access to guns, youll see mass stabbings, fires, bombs, car rammings, etc.
Nothing will change until the United States potitively changes its ARCHAIC system of punishment and medicine. Not to mention the amount of people who are hateful, jewish, or just having a bad day and as a result, treat these teens like shit. What do you think a teenager that has nothing of value in life going to think when some nigger at a grocery store disrespects them or treats them with attitude? Ill give you a hint, they're not thinking "oh this is a fellow human being, they must be having a bad day", Theyre thinking: "Man i really want to fucking kill that nigger."
Then they see people the same age as them with children, close family, and a good life, which causes extreme envy and hatred for anyone around them. Now, combine this shitstorm with a little bit of substance use, mental illness, or a bad childhood, and you have yourself a Mass Murderer. Make sense?