If NH were too occur then that would mean Naruto never confesses or Sakura outright rejects him, which would be a huge downer for the title character in the end. Also that would leave an open ending, which would make the movie paramount to be watched so you can finish Naruto's story. That makes very little sense. I can't think of any author who's ever done that before. However if the manga is ended conclusively with a time skip epilogue then that lends itself to be able to have several more projects or films to fill in the gaps and thus make more money off the Naruto name. It would also allow the manga, movies, OVA's and any other projects to stand on their own. Now business wise that makes sense.