Mass shootings happen in places other than schools. By your logic, we should see fewer in places with more guns among the general populace. So show us that data, and I’ll pay attention. But so far, I have no evidence higher rates of gun ownership is correlated with higher rates of safety.
I can’t look it up at this very moment, but I remember seeing a graph report showing that most major shootings happen in areas with significant gun control. This was back in 2019, so I don’t know if the stats have changed since.
I’m not sure what your source is, but the facts suggest the opposite is true. A 2019 BMJ study found that states with more permissive gun laws experienced significantly higher rates of mass shootings. But I’m sure the source of your graph is unimpeachable.