Sometimes, it depends on the section you're writing in. Some of them are so overflowing with stories (Star Wars) or have very little stories (Tintin) that getting readers and reviewers are rare. that said, I know a great people who also read something, but never, ever, review it.
The problem could also be to what your stories are about. Not only do you do a lot of crossovers with series that don't seem liked they go together, when someone reads something about, say, Star Wars, they're wanting usually familiar characters, ones that are part of the series and someone they can say 'oh, he was in this movie and had this role.' Having Original characters or characters that no one really is familiar with won't encourage much with readers.
Yeah, life isn't fair, or things would be a great deal different. The best way I could say for you to have OC or little known characters in your story and have people enjoy them would to start them off as supporting characters, having them take larger and larger roles as the story progresses. That way, you aren't having a story that goes 'Hey, everyone, read about this romance story with a character you know little to nothing about!'
Another way to do things is to not crossover things willy nilly. Try making sure they're in the same vein of worlds or features (Say.... Star Wars with Star Trek) or make the references subtle enough that someone could say 'hey, this is a reference to this' without beating everyone over the ehad with it.
Sorry, none of those are my fandoms at the moment. As for why people don't review, there are any number of reasons. In all honesty, I don't really leave that many reviews for the stories I read. I'm more likely to recommend a work than review it. Often I don't really have anything to say about it besides a vague, I liked it, which just seems like a waste of my time to do. Contrary to that, if the story is bad I don't bother reading it long enough to give a proper critique of it, so again it's kind of pointless to leave a review.
Apparently, there have only been thirty six stories on FF.N that I've felt the need to review in the many years I've been on it.
You seem to do a lot of crossovers. Sometimes that can be quite the deal breaker if the reader doesn't know both universes. Another thing that can turn people away is strange pairings. You will get a lot more reviews if you write a story with a popular pairing in it than an unpopular one. All in all, you should just write what you enjoy to write. Don't worry about reviews.
You seem to do a lot of crossovers. Sometimes that can be quite the deal breaker if the reader doesnt know both universes. Another thing that can turn people away is strange pairings. You will get a lot more reviews if you write a story with a popular pairing in it than an unpopular one. All in all, you should just write what you enjoy to write. Dont worry about reviews.
This isn't the right forum for discussion (that would be the writers forum - this is for posting fanfics) but like The Book Addict I'd wager the crossovers play a part.
Another thing could be that you seem to spread over a wide amount of fandoms. That means you have one shot in either of those fandoms and perhaps a few of the hits you get are interested in more of the fandoms you write for.
Me for example, I mainly read Harry Potter and Good Omen fanfics. If I happen to read a HP fanfic and see that the author has written more for those fandoms, then I'll read those stories too. Other fandoms? Nope, those I skip past, even if I like the author.
If you really want to put attention to your newest stories then I recommend advertising them in big letters wherever acceptable. This includes leaving in-depth reviews on other fanfics in that same fandom (I know I feel obliged to return the favour whenever possible) and spend a lot of time in forums talking with other fans.
I forced my way through the first chapter of "When Jaina Met Tumnus."
There's nothing to say about it. Nothing really happens. The language is clear enough, but reading it feels like an effort. It's not good, it's not bad, it's just...blah. that might not be why you're getting any reviews, you haven't been good enough or sucked enough to push anyone into that kind of effort.
1. Tighter language. Less words.
2. Lose the intro stuff. If I wasn't making it a point to read it, I would have stopped there.
3. I'm not sure how you post chapters, but depending on how fast your fandom moves, post one chapter a week on the same day each week. Gives the fic time to stay on the main page and net casual readers.
4. Have something happen. Stir the reader, don't just give weird little vignettes which are basically the author's daydreams. We're all guilty of it to a degree, but remember you're writing for others.