I lived in Australia for a year during COVID. It's surrounded by water and doesn't have thousand-mile long borders to any country. Controlling entry is not the same logistical problem as controlling entry to the US.

That said, a lot of US's immigration problems has been neglect to enforce immigration law, deliberate sabotaging of legislation throughout the years, and multiple broad amnesty decrees that basically broke the system. The system is broken by design and almost tailor-made to foment anti-immigrant sentiment that has sparked this new, ugly phase driven by unaccountable maniacs.