In short because Argentina was the go-to country for Nazi officials fleeing Europe after the immediate end of the war. Recent scholarship shows that this was deliberate policy of the Peron government.

Research of Uki Goñi shows that for one the Person government was highly sympathetic to the Nazis' anti-communism and hoped that escaped Nazi officials would be useful in building up intelligence networks against Communism world-wide thus furthering the political importance of Argentina in the coming Cold War (something the CIA did agree on). Peron hoped that his way he could place Argentina in a more important role on the international stage.

Additionally, there seems to have been heavy financial incentives for this policy from the German community in Argentina (the largest in South America at the time) as well as the Vatican, and the former Nazis themselves who had a lot of money put away in Switzerland.

The Argentinian involvement in establishing the Rat Lines is by now established and probably one of the main reasons why when it comes to possible countries Hitler could have fled to, makes it a likely place.

Sources:

• Uki Goni: The Real Odessa, Granta Books, London-New York, 2002.

• Richard Breitman, Norman J.W. Goda, Timothy Naftali, Robert Wolfe 2005. U.S. Intelligence and the Nazis. Cambridge University Press.