Because Nintendo's marketing team needs work.... a lot of work
most developers use songs for trailers. Heck even activision just straight up has top people make songs for its trailers and games.
Nintendo marketing is in a midset that licensed material is forbidden, but it would be nice to hear a known song through trailers for xenoblade or the like. Obviously not for all Nintendo games, but for the ones that are epic in nature, it would be nice to have an epic song to better convey the feeling







