Why Bioman and Maskman were used? there is a very simple answer: those teams were one of the few ones which haven't had yet a full Gokai changer; in the last episodes, most of the teams which had a full Gokai change had it for the first time (Flashman in ep 26, Timeranger, Megaranger in episode 24, GogoV in episode 23, Ohranger and Goseiger in episode 22); likewise, next week, Abaranger will have its first full Gokai change (even if all 5 already had a Gokai change separately); I expect to see very soon a Changeman full Gokaichange