I think part of it is that they want to feel like they can do something about it. It would shake them if they understood that gun control doesn't keep criminals from obtaining guns. To acknowledge that there is no (lefty) political solution to this problem would require a reexamination of their worldview. Then they might have to ask "Why?" Why are so many young men so pissed off? Why now are they shooting more when guns have been native to America since the founding? Could it be that the culture that the elites (whose ass they kiss) have been promoting is dangerous?

They always ask "why are they able to?" and never "why do they want to?"