The latest game is from 2011. Prior to that, the games didn’t present much story in-game either. At best, you had an intro, then the standard arcade mode, and the character’s ending.
Even if we do a 1:1 comparison, “Street Fighter” doesn’t necessarily have less storyline than “Mortal Kombat”:
“Mortal Kombat I” basically equals “Street Fighter II”: An “official” tournament where participants (enemies of the main bad guy as well as general martial artists) join for various reasons and where the bad guy will rule the world if he wins.
“Mortal Kombat II” is “Street Fighter III”: A secret private tournament held by some ruler for similar goals than the other tournament.
“Mortal Kombat 3” is “Street Fighter III: Third Strike”: Direct continuation of the previous plot, with the same bad guy, but this time not in tournament form.
“Mortal Kombat IV” is “Street Fighter IV”: A rather forgettable battle against a similar evil overlord than the one in the previous games.
The other games also just had excuse plots:
“Mortal Kombat: Deadly Alliance”: Shang Tsung and Quan Chi have joined forces and killed Shao Kahn and Liu Kang. They want to resurrect the army of the Dragon King. Fight them!
“Mortal Kombat Deception”: Shang Tsung and Quan Chi succeeded, but the Dragon King has returned. Fight him!
“Mortal Kombat Armageddon”: Royal Rumble!
There’s an equal number of storylines in “Street Fighter Alpha 2” and “3”.
The only reason why it looks like “Mortal Kombat” has more storyline is because they have some visually impressive intro sequences. But those are maybe five minutes of real time for each game and they only exist for the last three games anyway. The plot that happens during the game is presented just as vaguely as in “Street Fighter”, even in the later games.
Or can you tell from the game what exactly happened during “Mortal Kombat: Deadly Alliance”? Unlike with “Street Fighter”, you can’t even take the endings as references. For example, no matter if you play through the game with Raiden, Shang Tsung or Quan Chi, none of their endings even remotely resembles the things seen in the intro of “Mortal Kombat Deception”. (And in “Mortal Kombat Armageddon”, not even the game itself can be considered canon. The whole story is basically already told by the intro sequence. Fighters already die and Blaze has already appeared. None of the in-game action happens plot-wise.)
The amount of actual on-screen story prior to the 2011 game is easily matched by “Street Fighter IV”'s anime intro sequences and the countless dialogs in rival battles that are totally missing in any “Mortal Kombat” game.
And that’s, after all, not so natural in my opinion, as I showed above. Not even the mere presentation of the games is less story-driven in “Street Fighter” than in “Mortal Kombat”. The 2011 game was in fact the first one to ever present the story in a good way. But the “Mortal Kombat” community didn’t only start to gain interest in the storyline last year.
For example, some years ago, long before 2011, maybe 2006, I was on a “Mortal Komat” forum and asked what kind of tournament schedule they would come up with for the original game. Unlike with “Street Fighter II” where you can easily find fitting opponents, the “Mortal Kombat” one can be a real pain: Liu Kang, Sonya Blade, Johnny Cage and Raiden are the typical good guys, so it’s unlikely that they fight each other. Scorpion and Sub-Zero are canon enemies, so they should fight each other. Which basically means that you are left with Kano as an antagonist and he should fight against Sonya. So, you have Sonya vs. Kano, Scorpion vs. Sub-Zero and Liu Kang vs. Goro and Shang Tsung. Not much of a tournament, is it? But you know what? They actually tried. They actually came up with something. There was actually a discussion. And some months ago, I found a similar discussion on a “Mortal Kombat” forum, again concerning the first game fom 1992. Try the same stuff on a “Street Fighter” forum and take delight in people telling you that to them, a tournament is a very unusual way to portray the storyline of “Street Fighter II”.
Assuming that “Street Fighter II” has been remade as late as 2008, the disinterest can’t have to do with its age. When we are talking about “Street Fighter II”'s storyline, we are equally talking about a game from the early 90s as we are talking about a game from 2008. So, whatever the reason for the disinterest is, it has probably not to do with the game’s age.
Besides, if age is an indicator of how much the fanbase is interested in the story, then why did they specifically decide to remake the first three “Mortal Kombat” games for their movie-like game?
The story of “Street Fighter” is not necessarily worse than the generic storylines of “Super Mario” games. And yet, when you hear people talk about Mario or when they produce something creative, like a comic or a video, it will mostly include the plumber who rescues the princess and who uses mushrooms to grow taller etc. Except for selfmade artworks, what do you see when it comes to devotion toward “Street Fighter”? Combo videos. That’s like if “Super Mario” fan works would consist of nothing but speedruns and glitch abuse.