In 2008-2009, Pep started to give Busquets a try. There was really no place available for Busquets in the rotation, proven, famous, expensive players were ahead of him.
Pedro got his first playing time in 2008-2009, looked good. There was no place for him in the rotation at the start of 2009-2010, proven, famous, expensive players were ahead of him.
Thiago got his first chances in 2010-2011, looked promising. At the start of 2011-2012, two of the top three in FIFA player of the year were ahead of him.
Pep does not name his lineups based on resumes. Young players become regulars as soon as their play merits it.