Snoke’s origin could have been included as one throwaway line. Which begs the question why does anyone want it, because he was just generic evil guy no.27. He killed someone or did something, who cares. The end of ROTJ was eroded over 3 decades so of course things have changed. I’m sure the EU immediately ruined the “happy ending” too with a hundred despotic Empire guys and Dark Jedi weirdos.
And not everyone loves all the EU. Setting the scene is not a “throwaway” because it can be easy to do. I’m not saying a couple of lines would be entirely satisfying either.