This is the question you will be asking yourself about eighty pages into the novel, when you realize you've really only gotten passing references to Nostromo, and that all those references were nestled within the stories of English and American tycoons living/traveling/investing in Costaguana.
But just be patient—the story is very much about Nostromo, his downfall, and what he represents symbolically. We go over in crazy detail (we feel about literary analysis the way Nostromo feels about silver: obsessed) the nuances of both Nostromo's character and what he symbolizes: check out our "Character Analysis" and "Symbols" sections for more.