An agent might care about (and acausally cooperate with) all versions of himself that “exist”. MWI posits more versions of himself. Imagine that he wants there to exist an artist like he could be, and a scientist like he could be—but the first 50% of universes that contain each are more important than the second 50%. Then in MWI, he could throw a quantum coin to decide what to dedicate himself to, while in CI this would sacrifice one of his dreams.
An agent might care about (and acausally cooperate with) all versions of himself that “exist”. MWI posits more versions of himself. Imagine that he wants there to exist an artist like he could be, and a scientist like he could be—but the first 50% of universes that contain each are more important than the second 50%. Then in MWI, he could throw a quantum coin to decide what to dedicate himself to, while in CI this would sacrifice one of his dreams.