I think it's simply because, as sad as it is, DJ Grooves really just doesn't get as much spotlight as the conductor. Based on some unused voice clips from the Conductor, we can learn that apparently, at one point in development, BotB wasn't actually about both The Conductor and DJ Grooves, but rather mainly the Conductor, since he has voice clips implying that he would be the main NPC in every level, not just his own (voice clips for both The Big Parade and Picture Perfect) and Grooves was something of an afterthought. It's sad since I personally like DJ Grooves more, but it's the truth. Who knows, though, maybe DJ Grooves will get his well-deserved spotlight in the next game or dlc (if there ever is another game or dlc)
