It's a very different beast trying to police what's arriving into a country like Australia or New Zealand, where everybody arrives by air at one of five or so airports. Compare that to the EU with 500 odd airports, numerous sea ports, multiple land border crossings and a variety of border agencies policing it. Some countries have a natural geographic advantage.
And what is seemingly becoming the new Godwin's Law, that leads the conversation to the topic of Brexit. Part of the reason the Brits voted in favor, was to take advantage of their natural borders as an island nation to police what arrives. (Although for many is was more of a concern about the self loading freight arriving rather than that consigned to the holds).
...If only they could figure out their Northern Ireland issue.