^ Probably because their debut prep for EXO wasn't as successful as they wanted it to be. They're IMMENSELY popular now, but it was a popularity that mostly grew in the year to follow their debut. I don't think they got enough return from EXO's debut (or at least as much as they wanted) for the 129010329502 teaser strategy to be a real success. Hence part of the reason I think it took a year for EXO to get a first comeback.
Besides, if they just repeated that strategy here, they'd get hate for ripping it off or recycling it.
