Many rules of English grammar defy logical explanations. The rules governing reflexive pronouns are in that group.
myself, yourself, himself, herself, itself, ourselves, themselves
NOT I-self or me-self; you-self; his-self, he-self or she-self; we-selves or us-selves, they-selves or their-selves.
Looking for logical reasons to explain English grammar or spelling will just make you dizzy. Spend your time practicing.