One of the joys of a trope (or a cliché) is, as MemoryTale has pointed out, that it provides a shortcut to communicating something to the readers that can then be undermined or otherwise played with.
Without the trope, the author has to use up loads of words setting up the readers' false expectations, perhaps even risking making a narrator's inner thoughts look like a string of lies (or, in avoiding this, tie themselves in knots); using the trope, the author can encapsulate the set-up in as few as five words: "I am your father, Luke."
Without the trope, the author has to use up loads of words setting up the readers' false expectations, perhaps even risking making a narrator's inner thoughts look like a string of lies (or, in avoiding this, tie themselves in knots); using the trope, the author can encapsulate the set-up in as few as five words: "I am your father, Luke."