The story of Sub Zero and Scorpion is that they're titles, not individual people, who always end up fighting each other in MK tournaments. Their story centrally and critically revolves around the tournament. Who each individual incarnation is kind of irrelevant because the titles are the arch-enemies. Except when SubZero and Scorpion are besties, but we don't talk about that.???? How is the history of Sub-Zero and Scorpion not part of the plot and setting of MK? It's the backstory of characters participating in the MK story, it's why they're there, how is that not relevant or part of the story? Isn't the entire draw of fighting games the different characters and their interactions with the "main plot" being secondary to that? Fighting games show story from the perspective of the fighter you play as, how it's relevant to them and what their part in it is, I don't understand where you get your notion of fighting game stories.
Taking those two out of the tournament is like taking the crime fighting out of Batman. He's just a dude. Sub Zero and Scorpion without the mortal kombat tournament are just two dudes who don't know each other.