Same reason why many find Mimikyu adorable despite its appearance being literally "badly-drawn" Pikachu, while all of Gamefreak previous attempts and efforts at recreating the Pikachu magic on later gens ended in failure.
Same reason why many find Mimikyu adorable despite its appearance being literally "badly-drawn" Pikachu, while all of Gamefreak previous attempts and efforts at recreating the Pikachu magic on later gens ended in failure.
"Sometimes, simplicity is just the best."
This could apply to Mumei herself, her simpler design has its own charm.