Let’s cut through the garbage about so called “dual citizenship”...
I was born British, registered as a New Zealand citizen at age one month, but in 1975 I had to renounce my New Zealand citizenship if I wanted to be naturalized as an American citizen...
I raised my right hand and said the words “I renounce...”
If I had not done so, I would not have been allowed to participate in the naturalization ceremony...this was a requirement and part of the process...
There was no so called “dual citizenship” in 1975...
That meant all ties to New Zealand were severed and New Zealand was no longer responsible for me, an NZ citizen in a foreign country...(and I could no longer vote in NZ and now needed a passport to visit the land of my birth Plus healthcare was no longer free for me)
Now if there was a change in the American immigration etc laws since then, someone comment with proof and not just a story about some man you know etc...
The thing is, Australian law does recognise dual citizenship and has ever since the late 1940s when Australian citizenship first came into existence. Australia does not require a person to renounce foreign citizenships and it doesn’t happen automatically on becoming an Australian citizen.
You can lose a foreign citizenship if that country’s own laws extinguish your citizenship on becoming an Australian citizen. But Australian law will not deprive you of it.
You can renounce it - but the problem in all these cases is for various reasons, most of the people were unaware they even had a foreign citizenship. A couple of them probably should have been aware (if you were born overseas the possibility should certainly have occurred to you) but for the others - it’s more a matter of other countries giving out citizenship very easily to descendants of people from their countries.