First of all US is a democracy so the US government does what the people want.
The problem is gun control. Criminals love gun control because it means they can prey on unarmed vulnerable people.
Why does the US see these massacres in malls and schools? Not in other public places? Because malls and schools tend to be "gun-free" zones. So no one can defend themselves from lunatics such as this.
Virginia Tech specifically chose to prevent students from carrying guns on campus. The result is they could not defend themselves.
