The original purpose of Umbrella Company was to make money by selling chemical and biological weapons. They were unexpected and did not want to see Resident Evil happen. As you said, it is meaningless to get a planet full of zombies. The screenwriter of the movie is absolutely brain-dead. He went directly to shoot a global Resident Evil, and the later scripts could not be edited. Let's honestly follow the plot in the game. This film is completely untrue.