Im just gonna point out we as a culture have been dealing with this problem of just random acts of violence for quite awhile, its just that what came before mass shootings is kinda glossed over / forgotten. Before the mass shootings we had bombing campaigns, the una bomber being the most notable. Its just that unless it was really big it rarely got all that much attention and due to how everything was disconnected at the time unless you were the FBI you may not have even noticed it was a thing.
The problem is that the Columbine mass shotting and rise of cameras kinda killed off the mass bombers. Also Columbine happened right when this shift was happening and thusly became the standard for what people do. If it was instead some dudes shooting up a police station I suspect that would have become the norm.