You are correct in thinking that there would be an infinite subset of universes where humans never evolved. However, there would also be a much smaller, but still infinite, subset of universes where humans did evolve. And there would be a muuuuuch smaller, but still infinite, subset of universes where the history of the universe and all of human history transpired exactly as it did in our universe, up until the point it diverged with the necessary changes in order to be relevant to the plot of the movie. That tiny tiny tiny subset is the only thing we talk about in movies, because otherwise it would be too confusing for general audiences. Hope this helps.