I think the NSMB series unfortunately sucked some of the enthusiasm out of 2D Mario, they milked the shit out that same tired formula (NSMB, NSMB2, NSMBU, Mario Run) and damaged the franchise in doing so, while Wonder tries to break out of that mold, it isn't enough of a step beyond I think. Sure the games still sell well but obviously we're not seeing the same kind of increase for 2D Mario as we have seen for other Nintendo franchises like Zelda and Smash and Animal Crossing.
Mario Kart for one is clearly the lead selling Mario franchise these days, even in the movie, a huge chunk of the film is basically a commercial for Mario Kart.