"These kinds of events" is cherry picking. Violent gun crime, gun deaths are trending down and have been for decades despite the assault weapons ban expiring during that time. As awful as events like these are, statistically they are extremely rare, even with mass shootings knives still kill many times over more than AR15s and all other rifles combined. Yet the anti-2A'ers will move heaven and earth to change gun laws and further restrict my rights while having zero fucks to give about knives or other things that kill us in far greater numbers.
I don't think it's really true that those things are 'trending down and have been for decades'. They shot up dramatically during the 60s, stayed high during the 70s and 80s, came down equally rapidly in the 90s, and have since more-or-less flatlined at much the same level as before the '70s rise (having gone down a bit then recently started going up a bit).
It seems a hell of a puzzle why murder and violent crime in general was so high for the period '65 to '95 though. And not just for the US, to greater-or-lesser degrees, the same pattern occurred in all developed countries.
(I'm inclined to blame lead in petrol, myself, but maybe it's some deep sociological thing to do with non-linear responses to increases and decreases in wealth or social and physical mobility?).
Clearly it's true that there are many other factors in violence and murder than availability of guns. But that's not much consolation for those mourning their children. A preventable death is still worth preventing.