What's more is it doesn't necessarily work. Personal anecdote: my high school practiced lock-downs and then an 'incident' occurred and it was every man for him/her/theirself. We ran into classrooms and locked the doors and hid. It was not at all as practiced. Then there's not a lot of credible research (though there are some recent nuanced findings that look at HOW such procedures are done) that suggests these do more than, as you note, normalize a traumatic idea for young students, e.g., https://www.everytown.org/solutions/active-shooter-drills/, https://www.tandfonline.com/doi/abs/10.1080/15388220.2022.2162533. That said, the issue still remains that school shootings can probably be stopped most often before they happen if effective social/community conditions are implemented. My personal favorite is this database, where a researcher forensically evaluates the long chain of events that often lead to school shootings: https://k12ssdb.org/