The universe doesn't decide. Humans decide. A million choices freely made by humans determined to bring harm against fellow beings decides when and where and with what frequency these things happen.

"Randomness" infers a lack of will or control. The truth is, humans control all the choices and actions that lead to the slaughter. It's not even unpredictable. I mean, what do we expect to happen when fear and hate are rampant, and there are more guns than people? The outcome is entirely predictable, and therefore not random.