Starfleet's uniform and hair code is a deliberate imitation of the American military, even though it's not an organization of Americans, or even humans. Worf and AU Neelix were obviously allowed to wear traditional Klingon/Talaxian hair, but Worf's privilege came over time and Voyager was stuck in the DQ. At least after Ensign Ro, Bajorans were allowed to wear their earrings.
