I think they're holding off on the trailer because despite the star power of Pratt and Lawrence, they're not going to try and sell it as a popcorn blockbuster but as a prestige blockbuster (aka, an awards movie) and thus they'll focus the marketing entirely on awards season.
Also, word is that Passengers is one of the biggest victims of a court ruling that prevents Digital Domain from completing any of its MOVA motion capture technology because DD was midway into its work on the movie and thus the studio had to scramble for an alternative. Depending on how much of the film incorporates the MOVA footage it could explain the lack of a trailer also.
She is arguably the most popular young actress amongst the biggest audience of movie-goers (teenagers), that's why she's getting an astronomical push. I mean, she probably sucked some dikks here and there as well (there's quite a bit of rumors about her "work" relationship with David O Russell) but you don't get to be in every movie if you don't make the right people a lot of money.
