>If it's such a "complicated issue", why did the frequency of mass shootings in Australia drop to negligible levels after they took the simple step of enacting a comprehensive gun ban?
It appears largely because the gun ban simply changed the method by which massacres occurred. Using the list from here (https://en.wikipedia.org/wiki/List_of_massacres_in_Australia), using the Port Arthur shootings as the pivot point for a 25 year look back and forward, we find before Port Arthur ('71 to '96) there were 123 people killed in some form of multi death incident and a total of 22 incidents. After ('96 to april '21) there were 146 people killed in 37 incidents.
There are some issues I take with that list as a whole, for example for this discussion familicide probably doesn't really enter into it, or a number of the incidents include the perpetrator (which I have tried to filter from the numbers above). If I try to cut the values down to just non-familicide incidents, it looks like 88 deaths in 16 incidents prior and 89 deaths in 23 incidents after.
Admittedly yes the raw number of shootings did go down. But at least to me, that would be a cold comfort to know a dead relative or friend was burned to death rather than shot. If the end goal is to stop people dying by firearm, then fair enough, Australia's laws appear to have done that. If the goal however is to stop people from being killed or attacked in senseless acts of violence, then I think these numbers make the argument that killers will kill with whatever tools they can get their hands on and the issue is indeed more "complicated" than just making one such tool illegal.