Actually you are wrong. Australia allows citizens to leave on any passport. I often arrive on my Australian passport and leave on my Taiwan passport. The U.S. allows the same. In fact recently a Taiwanese woman kidnapped her kid and took him back to Taiwan by getting a Taiwan passport without her American husband knowing
@@petercomfort9651 This is like claiming “You are ALLOWED to drive over the speed limit and make illegal U-Turns. I always do that, never had a problem”. No, you are just lucky that you haven’t been caught yet. The US laws definitely do not “allow” this behavior, the border control probably didn't bother to enforce it because they are focused on more important issues, but don’t take it for granted.
This happened to my son whom was born in Taiwan but when we were leaving Taiwan with his Australian passport when he was six months old. We were told that he needed Taiwanese passport to leave Taiwan. We ended up changing the flight dates and applying an express Taiwanese passport. Luckily it wasn’t too expensive.