Because the serie still need to be accessible to newcomers. And I personally feel that the movies scream "cut content here and cut content there" with these weird text summary that break the immersion. In days, you need to play the actual missions to understand how eating ice cream is rewarding. In re:coded, the fun aspect (there isn't much) is to explore worlds you already know looking for bugs. The movies are a good summary, but that's all they are: summaries. A serie complex like Kingdom Hearts, where all episode are mandatory deserves more than summaries for its storytelling.