"The norm"? How so ? I see outliers.
Spoiled, troubled white kids with semi-engaged parents providing LOTS more material stuff than emotional guidance and stability. Parents on their chosen treadmill of life or in over their heads as the product of a similar dynamic themselves. Raising disaffected boys that feel ignored, helpless, marginalized, devalued as white males, and then more influenced by entertainment and pop culture nihilism than anything else in their lives - to the point of mental illness characterized by a feeling of despair and futility. Many kids have the symptoms, some few turn such self-loathing outwardly, assigning blame to others. I believe that happens as a perversion of the pop-psych "self-love doctrines" presented as a cheap ego booster in the godless attempts to gin up self-esteem.
Genuine self-esteem is actually a product of self-acceptance, something religion USED TO provide within 95 percent of American culture. "Stuart Smalley" ain't filling that void. Neither is some dumb-aszed pop psychology formula.
Maybe CRT-sourced SEL and some divorced families with dads driven away by mom (or just plain loser "sperm donors") will "create" more at a fast enough pace that we can call it "the norm"? Time will tell.
Anyway, that seems to be the common thread among school shooters, as I observe. ?