Thanos snapped out half the universe in Avengers: Infinity War, but all six of the original Avengers survived – why?
The six founding MCU characters, along with several independent-operated heroes, spent five years following Thanos’ downfall at the end of the Infinity War in different circumstances. Tony Stark reviewed his superhero role and lived a quiet family life with Pepper Potts (Gwyneth Paltrow) and Morgan. Thor, who was guilty of failing to stop the Mad Titan, was depressed as he retreated into New Asgard. Meanwhile, Captain America and the Black Widow were active in duty – the former participated in treatment sessions, and the latter took care of the rest of their allies. Bruce Banner worked to become a Smart Hulk; And finally, Hawkeye took on his new personality as Ronin to deal with the death of his family.
The Endgame meant to be the final film in the Infinity Saga, which proved to be the swan song of some of these heroes, eventually. Russos also co-authored the story with Christopher Marcus and Stephen McFeely, selling the idea that the heroes mentioned above would survive the destruction.
Mad Titan’s intention wasn’t out to murder anyone. This is evidenced by his initial confrontation with the Guardians of the Galaxy, when he used only the Reality Stone to stop Drax and the Mantis from attacking him. It is the same when he meets Guardians of the Galaxy and Iron Man, Doctor Strange and Spider-Man again in Titan. With him having the three crystals, he could have killed these heroes easily, but he didn’t. He only killed to get the Soul Stone and Mind Stone.
Also, because of the huge cast in Infinity War, the shoots were done in chunks, with only few cast. So, there weren’t a lot of fights happening around. Since Thanos’ snap is random, Marvel Studios is easily able to come out with the explanation that Avengers was lucky to get saved. Fans, of course, know that this was done to keep them motivated after Avengers: Infinity War till Endgame. The story, however, justifies their survival.