There seems to be a slight misunderstanding here: If you imagine the “moment before” the big bang that is a state where the entire universe is compressed into a singularity, which necessarily has no entropy, because it can only have one state. Once the universe started expanding, you get a whole lot of disorder, because, while you are forming particles (introducing order) those particles are moving away from each other at relativistic speeds. The available volume for the particles (the volume of the universe) increases extremely rapidly, meaning you have more possible microstates than if all particles were compressed into a point.