The State Department ensured that Somoza did not kill him.

From Small Wars, Faraway Places by Michael Burleigh. Page 414.

Paradoxically, the foundations for the remarkably untroubled modern history of little Costa Rica were laid by José ‘Pepe’ Figueres, who seized power from a democratically elected president in 1948 and promptly abolished the army, nationalized the banks, and granted women and blacks the vote. Despite being a rancher, he also instituted land reform. What he did not do was indulge in strident anti-yanqui rhetoric, for he had studied at MIT and had two successive American wives, with the result that, although balefully regarded by the CIA, he was the poster boy of the State Department, and Costa Rica became an island of peaceful democracy surrounded by variously extreme anti- and pro-US guerrilla movements and dictators. The State Department ensured that Somoza did not kill him.