I haven't seen the movie yet (sometime this week), but I was
   thankfully aware of this sinister side the never-ending sequels
   in mythological universes. You can have your great victory but
   not your happily ever after UNLESS you're willing to write about
   a functioning society with an ever-lasting peace: a Utopian
   vision in great detail. Not easy to do at length for then every
   conflict must eventually be resolved or be so minimal as to be
   cute and sugar-y, a true contrast to the drama of world-ending
   Sagas but one that the audience will not typically tolerate. I
   would enjoy such a reading because I find contrasting Utopian
   future visions to be fascinating in measuring their practical
   value vs little things like... I dunno... basic things like
   greed, sociopathy and such... but I suspect a majority wouldn't
   stand for it.