Because anybody who comes close to that ideal target already knows that they're putting chemicals in the water, and won't be susceptible to their pharmacological tricks. The methods used to destabilize minds include hormones and "depression" drugs, which apparently contribute to ongoing dysphoria, suicidal tendencies, and psychotic breaks. Many of these shooters were already known by police, and almost all are on something -- the black FTM (they're almost always black) was obviously on high-dosage testosterone therapy, which will do this.