Didn't make enough money yet. To be worthy of a ride you need to make a billion dollar grossing movie (like Frozen) or a series of movies that can reach a billion dollars (like Toy Story)... Otherwise you're not worthy.... Coco has not even reached the minor attraction level of Lilo and Stitch.... So when Coco gets a sequel or sells a half a billion in toys I might expect Disney to create a ride for the show... until then why create something as expensive as an attraction when the movie will likely be less memorable than Gummi Bears.
Yeah... that's not true at all. Alice, Ratatouille, Song of the South, A Bug's Life, and TRON would beg to differ.