That's because, in 1955, there were over two million deranged nutcases locked up for life in state mental hospitals, where they belonged.
Now, when there are a LOT more crazy people, the state hospital population is around ten thousand.
Until we start practicing nut control, gun control is fruitless.
I predict, right here, that the shooter (whoever he turns out to be) was 1) known to be crazy, 2) known to put people in fear, 3) known to the authorities, and 4) that no one did anything.
What we are dealing with is outright spiritual warfare, dealing with the demonic.