Most likely because this is Nextar Ent project and EB is their artist. If this is CCM's, ofc artist line-up would be very different.
I have to hand it to Cho Young Soo. That guy really knows how to make a song. IMO this song isn't far shy from the greatness that is Day by Day or Cry Cry. And the Park sisters really had an amazing vocal quality aren't they? CCM need to seriously considers making them a sub-unit.