Aren't you tired of so many "demons"? I mean, everybody knows how Estefanía Meyers and her literary saga bastardized the vampires and lycanthropes. So authors with even less talent try to recreate her success using other classic monsters. This leaves us to a "who makes the biggest shit" contest:
-My novel has humans, ghosts and demons.
-I see your bet and I add a demon-girl who felt in love with a vampire half ghost with a cyborg cock.
Since the new authors (novel, comic, manga...) haven't enough creativity to... I don't know... maybe inventing new monsters, the same way as our ancestors did? They use the "maximum exponent tabu": the demons.
From a commercial perspective, it makes sense using old concepts that everybody knows to have the easiest target. It's what Hollywood has been doing last decade, literature and Internet are only taking advantage of the pull to be lazy.
Demons are the easy target because nearly every religion and mythology have a devil antagonist. You don't need more than a half neuron to realize that's the indolent way to "make cool characters without effort". You will still have fans fan-tasizing with them because their hellish magic powers.
Why should I put effort on making a reliable character if I can make a half-demon wizard warrior with ninja guinea pig powers?
Each media bastardizes as it can. It's common seeing this type of characters having romances or love triangles in young-adult novels. Comics, mangas and videogames had devil-humans with dignity like Spawn or Dante (I only know them by name). But now they became a stereotype when someone wants to make something "big-interesting" and they don't know how to do it.
Hey, I'm not speaking of everything. For example, there are comedies that know how to use them as comic relief: South Park, Leo & Satan, Pesadillas del Infierno… And of course, when this characters aren't made to make laugh, they try to insert you the concept through every hole possible thinking that's how it's done to be respected.
Nowadays, we have even devil hedgehogs and ponies! The circle will be full when Hollywood adapts any of this stories and it has such a massive success that TVs will produce more versions and trash media. What's more, I bet they already did that, but I don't know those franchises. With so many Meyers wannabes, it's impossible not to be tried by a desperate. production company I hope future projects like those to burn and disappear without a trace.
And what can we do?
If you call yourself a creative person, I suppose you thought a twist for a classic concept. I speck about any format: drawings, stories, vignettes, shorts, fangames…
In that case, if you feel hinted with the previous statements, you're doing it wrong. It would mean that you felt into the cliché of any fanboy. But don't get down, noticing this is the first step to improve. I personally ask you to investigate how NOT to do it. Since there isn't any wolrdwide known "demony" who can serve as reference, this concept will be overexploited until somebody nails it.
That's how everything works, PewDiePie and Smosh weren't the first youtubers making videos about games or shorts, but they had the luck to stand out over the rest. Now they have thousands of imitators all over the world trying to join the "trending topic".
If you have enough intelligence to catch this references and read until this, don't conform with taking the trending bus and "waiting to stand up". Just create without recycling, fame and recognition will come over the time.
It's a slow and hard process, but you won't forget it this way. And if you fail, it would be only a little passing phase in your career as a creative person.
Don't let the dolphin-pony be better than you!