I wasn't in the room for decisions so I could be a little off, but as I best understand it, for a while it was thought that it'd be easier for actors to do the semi-scripted dialog (see @TheNextStepDance's recent answer about ad-libbing) if characters were named after the actors, because sometimes actors would accidentally call each other by their real names during scenes and ruin the take. Starting with The Next Step season 3, new characters were named after the actors. The original pilot for Lost & Found even had the entire cast going by their real names. But it became important to keep track behind the scenes of when people were talking about the actor/real life and when they were talking about the character/the story on the show ("did you hear about how Shane..."). So except for some dancers on The Next Step who I think they just really liked the names of, characters were renamed, which I think was decided after season 3 filming was over but only a few episodes had aired. So through changing voiceover and on-screen graphics, or shooting new talking heads, the band was renamed from Alex, Shane and Levi to John, Luke, and Theo.