New Zealands new gun laws

So after the shooting New Zealand took action and made stricter gun laws:

So my question is: Why do you think it is hard for countrys like the US where shootings are way more common to change its gun laws and do you think that they should take example from new Zealand and do something about their own laws?

I personally think that stricter gun laws are already way over due and I really hope that this might give the US at least a little nudge in the right direction.