Every good story needs Conflict, that's axiomatic. But to simply have The Protagonist fight The Antagonist would not suffice. To provide the tension necessary to drive the audience from the opening to the end of the story, the author must increase the Conflict gradually over the course of the story. This is Rising Conflict.
Seeing as how it is almost mandatory that the confrontation between protagonist and antagonist not happen until The Climax, the story has to rely on lesser sources of antagonism in the meantime: fights with mooks, mini bosses, and dragons may all provide the proper amping up needed to deliver a fully charged climatic battle between the protagonist and the antagonist.
But not all movies have classic villains, and as such the protagonist may simply be struggling against mounting complications and obstacles that get between them and their goal. Hence this trope is also frequently called Rising Complications or Rising Action, putting the emphasis on the protagonist's struggle instead of some clash between good and evil.