It's a lot harder to kill people with things that aren't guns. If it was as easy then soldiers would primarily equipped with "knife, or acid, or poison, or fists". The army chooses guns as the primary weapon are they are clearly much more effective at killing.
Remember the outrage when Syria did use poison?
I'm saying that if the army shared the goal of mass shooters - to kill as many people as possible indiscriminately - guns would absolutely not be their weapon of choice; and if the army switched weapons from guns to poison, the magnitude of violence would be amplified, not reduced.
Fortunately that means they use guns instead of more dangerous weapons.
Then when you trial date comes up it all goes on again - so these people see the fame that others have gotten - and how people have loathed them and feared them, and their shots are heard around the world.
Not so much the case when someone mixes bleach and windex.