“A Nature Carol” shows a future where Hal, Daisy, and Squeeks no longer live near or interact with Nature Cat. This is sad enough on its own, but consider this: Daisy and Hal are pets and can still live inside. Squeeks is a wild animal whose habitat was destroyed in this timeline. She very easily could be dead.
Made even worse when Future Hal comments that Daisy and Hal moved but says that Squeeks “isn’t around anymore”. No wonder Nature Cat cried.