For an example: let's say I begin my story with a man being murdered. Next scene, the main character begins with either "Last night, my father was murdered." or "Last night, a man was murdered."
Even though both lines are nearly the same, with just a few words swapped, they both establish completely different things about the setting; they both give us a different understanding of the situation the mystery's being built upon.
Hell, you can add another layer of mystery with the latter line; if I have the main character be like one of those obsessed cops, the latter line can mask his motivation. Either he's like that because of an earlier failed case with the same criminal, a similar case, he's just obsessive like that, or perhaps the victim was very close to him?
And even if I don't go for that second layer and use the former line, the mystery works just as well. The mystery is still "who murdered Person X and why?". It doesn't take anything away from it, while at the same time giving us some understanding to stand on.
That's what we're asking. Something to understand what's going on, a common ground, something to give us a reason to care for the story and be curious about the mystery it presents. As it is, there isn't any of that.
And, before you say it; no, just because it's OC-centric doesn't mean it's bad. I've seen a couple of good Nasuverse fics which center on OCs and/or go outside the known established stories. But what sets them apart is that, despite having no ties to canon characters and doing their own thing, they still FEEL like a Nasuverse story. They do an excellent job in establishing the setting and thus people can relate to them. It also helps they're very well written and thus enjoyable on their own.