Because now everyone will pontificate as though they know the mindset of the perpetrator, the circumstances surrounding the event, the pain of losing a loved one in such an event, etc. They will run around like chickens without heads, the media will open itself up to so-called "authorities" on the so-called "criminal mind," and in the end, a video game or movie or faulty gun control law or musical performer will be blamed for this and we will, once again, learn absolutely nothing about the society in which we live except the same old meme, "it's screwed up, what can you do?"
Again: I lol'd. It may be a cold response, but it's the most honest one I can give. I felt the same way about the Columbine incident. We learned nothing from that little fiasco, either, especially not any sort of social reform within the school system.