The US has a lot of community transmission so it’s not just about international travel. Also, Canada, Denmark, Finland, Japan and Norway are developed and have much fewer Covid related deaths per capita than the US.
The fact that Australia is “mostly empty” doesn’t actually help your position either because it only demonstrates that the majority of the population are concentrated in a relatively small area, where community transmission would be more likely when not accounting for other factors. Also, Australia’s smaller population is not directly relevant when considering deaths per capita.