They already have, but you never heard about it, because you're not going to hear about the kids who fail to get their hands on a gun and decide to give up on their school shooting plan. School shooters are real people, not villains from movies who are endlessly determined, resourceful, and devoted to hatching their evil scheme. More often than not, they are high school kids in mental anguish with very troubled mindsets.
Yes, some situations are going to arise where the laws fail to prevent the crime, that is, after-all, why we need laws. My problem isn't necessarily with steps taken to make school safer, but the refusal to admit that strengthening or creating new laws is helpful. It has proven to be so.
https://www.sciencealert.com/scientific-evidence-that-stricter-gun-control-works-saves-lives