I blame Aquaman.
EDIT: nah....that's really a cop out. The real honest truth is that Injustice has always felt a little bit like the redheaded stepchild of this community. Part of that has to do with actual relevant issues surrounding the games mechanics. Not to say they're necessarily even bad, but you can at least see how some people might have frustrations with them (Aquaman, walkspeed, aquaman, interactibles, aquaman, grab immunity, aquaman, ambiguous crossups, aquaman, etc.).
That being said....I also genuinely believe that a bigger part has to do with the fact that a lot of people on this site just plain have a bigger attachment to the Mortal Kombat universe than the world of DC comics....which as a fan of the later is rather sad to me.
I think MKX will be very good, but hypothetically if it were a weaker game than Injustice I still think it would have more interest at this point in its life than Injustice does just because of the legacy of MK. I don't necessarily even think that's a horrible thing...but as an injustice fan it does make me sad.
Consider: people joke right now about how nobody cares about Injustice because "who's next" and everyone has a laugh. 2 years from now when Injustice 2 gets announced if people make similar jokes I wouldn't be surprised if people get flamed for it.
For my part, I sometimes wonder if maybe I could have done more to support the game and my main. Most of my time here has been spent learning basics and I've not felt particularly qualified to develop or discuss advanced tech for them. Maybe I should try though....not like it could hurt at this point I guess.