Why doesn't Fortunato ask why Montressor is burying him alive in "The Cask of Amontillado"?
The easy answer to this is that Fortunato as a character is just there to function as a part of a metaphor. Some people say that this story really is a metaphor for Montressor performing a black Sabbath (see the first link below). Other experts have suggested that since this is told as a flashback, that Montressor is unreliable or might even be making this all up. I've even heard the interpretation where Fortunato is nothing more than a part of Montressor's personality that he is trying to "bury" metaphorically because he doesn't like himself (which is an interpretion touched on in the second essay I linked).
If you want to see this as a story and not as an extended metaphor, I think the best answer is that Fortunato is in shock, still quite a bit drunk, and not thinking clearly. And when Montressor is down there adding his screams to Fortunato's, it's probably quite clear that Montressor is enjoying this murder, so the only way for Fortunato to "get" Montressor back is to deny Montressor the communication the man clearly wants. By remaining stubbornly silent, Fortunato can deny Montressor some pleasure.