After your forced gun buy back, your gun laws relaxed. There are as many guns in the hands private citizens in Australia as there were before the buy back.
You also don't have the population of the United States. As of June 2020 Australia has a population of 25,687,041. In the same year Los Angeles, Ca metro has a population of 12,447,000 or a little less than half of the population of Australia. The United States in 2020 was 331,002,647.
If Australia had the same population of the US then you would an equivalent mass shooting and school shooting rate.
I'm not trying to disparage Australia in anyway. I've never been to Australia but from what I have seen I think I would love your country. I also have friends who live there. My only problem with Australia is that it seems like every animal, sea creature and insect in your country wants to kill you. Plus you have crocs as big as a 747 airliner. And just when you think your safe a kangaroo will come and kick your head off of your body. :)