[mudsliptones]

most horror movies are aside from the effects and acting, timeless
the zombies from night og the living dead to the ones in resident evil change, but the concept "zombie" stays the same
it's just, people still hold on to those monsters (zombies, demons, ghost, vampires)
why you ask?
I wouldn't know, long ago there were people who "invented" the zombie, vampire, demon, ....
lack of originality nowadays?
maybe
the only thing that does change is the looks of certain creatures, like demons
the possibilitys on better FX and the fact that more is allowed these days gives you a different look then lets say in 1975
example, earlyer just a dude with some make up was a demon, wooden horns on the head and a rubber tail maybe

now: we see a young girl, half naked, bleeding cuts in her face, that stuff

I guess that people are getting tired of the old looks of monsters and are not scared of them anymore
If you look at night of the living dead it's not scary, but back then it was
also...hollywood, they want new stuff, but instead of inventing new creatures they just build on the classics (dracula, zombie)
and just make them bigger in looks, scaryer

that's about it