When people hear "school shooting", they're generally envisioning something like Columbine - an event with a large number of casualties, targeting students as a group, and lasting until the shooter(s) is killed.

They are not thinking "drive-by gang shooting at 9pm that happens to be on or near school property". They're not even generally thinking "student kills another student after argument."

Labeling all of these categories (and more) with the same label leads to emotionally-driven political opinions and policies, which are often inappropriate and not proportional to the actual problem.