there isn't some larger political movement to tighten these laws.
Every movement that starts is overshadowed by NRA countermovements. Huge numbers of rural, conservative Americans believe more guns means less shootings, and no evidence, facts, or even the death of their own children will dissuade them.
that is a terrifying ideology.
That's exactly the problem—ideology. Putting theory above practice. These people hold the theory that more guns means more safety, and they base their beliefs and actions on that theory, not on the practical, real world, in which their theory is simply not true.