There is some truth to that, but many of the top Australian players did play college ball - mostly in the U.S. Among those who played for U.S. colleges are Andrew Bogut, Ben Simmons, Patty Mills, Matt Dellavedova, Luc Longley, Andrew Gaze, and Cameron Baarstow. And a number of others, such as Daniel Kickert and Brook Motum, were stars at U.S. colleges before returning to play pro ball in Australia. St. Mary's currently has six Australians on their roster, and they have had at least one - often more - on the roster for 18 consecutive years.
I don't count Kyrie Irving, but he was born in Australia and is a citizen of that country.