Because Julian Assange was on UK territory, not Australian.
Espionage:
https://en.wikipedia.org/wiki/Capital_punishment_by_the_Unit...
Otherwise there would be a booming naturalization business for some less-scrupulous nations.
>some less-scrupulous nations
Like the US, where you can buy your "out of prison" Card?
https://www.swissinfo.ch/ger/auslieferungs-gesuch/2803478
Argentina asked Switzerland to extradite Jean Bernard Lasnaud for smuggling Weapons to Ecuador and Croatia (he's French), and why Argentinia? Because the former President Carlos Menem and other Politicians where involved in it.
As an example, France would ask A if he can extradited to France and prosecuted there, even when let's say the crime was in Country B. The US did something like that with Otto Warmbier:
https://en.wikipedia.org/wiki/Otto_Warmbier
That whole thing is often not National or International Law but Diplomatic (especially with someone like Assange)
That's Argentina asking Switzerland to extradite a French citizen to Argentina for crimes committed under Argentinian law. The article does not say that France was asked for their opinion or permission.
> https://en.wikipedia.org/wiki/Otto_Warmbier
That's the US asking North Korea to release a US citizen jailed there for a crime against North Korean law. Extradition does not enter the picture at all.