Choi Jung Yeol, the director of upcoming movie 'Glory Day,' revealed the reasoning behind his decision to cast EXO's Suho (Kim Jun Myeon).  

During the recent press conference for promoting the movie, he said, "There were two reasons I cast Kim Jun Myeon.  I believed there was deep significance in the act of continuously discovering young actors alone.  I had an ambitious desire to meet an actor who could bring forth the future of Korean film.  Also, if I were to cast a star, I had an ambitious desire to shatter the normal image [that star] has.  

"In Jun Myeon's case, both those reasons properly matched up, but I wondered if the viewers would enjoy it if the role of the poor Sang Woo was given to Suho of group EXO, which is flashy, cool, and provides a fantasy for their fans."

That's probably why it took him so long to finally cast Suho!  You can see if it was all worth it with the March 24 premiere.