Because they are not rappers. But they did it well. I love the part of kyuhyun sang " nae-ga jugil nomiji mwo uri-ga eo-geunnal-ttae-myeon
jeonbu nae tashiji mwo machi jwehinin geotcheoreom
nan hankeo-reum mu-lleoseoseo amu maldo anhae
wahnbyeokhan neohante nan hangsang bujokhan saraminkeol