T-ara they all switched leaders. During their debut it was Eunjung 2009-2010 then Boram 2010-2011, Hyomin from summer of 2011 till december, Soyeon from december 2011-2013 and Qri from 2013 and is still the leader now. Jiyeon is the only member that was not a leader since she was a maknae. If I remember correctly the CEO did this to see who would be the best leader and see how they handle things individually as leaders. Hyomin her time was probably so short due to her being way too shy and not able to take initiative to speak up.