We absolutely had these shootings in/around Seattle schools in the '80s-'90s, I should know since I was attending a Seattle high school when Columbine happened.

I presume I don't have to explain gang related shootings to you but they were an issue then that has improved but hasn't disappeared since the same social issues at their root still exist. If you haven't experienced sustained bullying/cruelty accompanied by indifference by teachers and administrators who choose not to intervene it's going to be difficult to explain why I didn't find Columbine shocking.