The reason is simple: when parents see their children playing major works, they feel that their tuition money hasn't been wasted. Moreover, judges at competitions award extra points for difficulty. And the difficulty of a piece played as part of the admissions screening for middle- and high-school music programs is also often a decisive factor.
理由很簡單，家長看到孩子彈大麴子，會覺得高額學費沒有白繳，比賽時評審委員看在曲目艱深的份上，會多給點鼓勵分數，甚至考國中、高中音樂班甄試時，曲目的難易往往可以決定錄取或是落選。