Did you have a massive anti-gun control "but mah freeeeedoms!" public and political party fighting against this sensible act?
There was political consensus which resulted in 700,000 semi automatics and handguns purchased by the government, handed in or confiscated.
https://www.sydney.edu.au/news-opin...es-revealed-25-years-on-from-port-arthur.html
In 1997, the year after the Port Arthur massacre, Australia had 6.52 licensed firearm owners per 100 population. By 2020, that proportion had almost halved, to 3.41 licensed gun owners for every 100 people.
Mass gun massacres ceased after this.