I may not have seen much straight up advertising for the movie, but I have seen a lot of merchandise for the movie. It makes more sense when thinking this way. You gotta remember, MLP is first and forenost a toy based property and Hasbro is a toy company. They probably want to focus on advertising through the toys. Which yeah is odd by a movie perspecive, but I never predicted this movie bringing in big numbers anyway.
And I wouldn't go as far as say the movie is gonna get canceled. It would be really awkward for that to happen now, especially after the art book, the junior book, the official movie concessions, and the many toys have already been released for it. Unless something really controversial happens involving the movie or someone involved with it in the coming weeks, then I wouldn't worry.