I am a dual (Aust and US) citizen and live in Australia. I have never been to the US but Mum is American. My bank wants to know...?

I am signing up for a new bank account here in Australia and the bank wants to know if I am am a US citizen. They say it's for taxation purposes. Why are they asking me for my social security number? Does it mean that I'll get taxed more on my income once I start to earn money? I'm currently a... show more I am signing up for a new bank account here in Australia and the bank wants to know if I am am a US citizen. They say it's for taxation purposes.

Why are they asking me for my social security number? Does it mean that I'll get taxed more on my income once I start to earn money? I'm currently a university student and have no clue about this.

Also, my mum told me to never cancel my US citizenship and that it is very valuable should I ever want to live over there. Is there a downside to dual (US/abroad) citizenship?

I need some answers...
Update: My bank didn't ask me this 10 years ago, why are they asking me now?
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