When something is done well it gets copied and becomes a cliche, then it's no longer scary. Old movies are where the cliches come from, so revising them no longer packs the surprise and unknown from when they were first released. The movies you watch today might be scary, but in a few decades when they've been mimicked a few times they will no longer hold that potency.

So, in a way, yes, older movies tend to no longer be scary. I think some of it is also learning the film making techniques. When we watch the behind the scenes of an actor in a suit, it makes the film lose some of that unknown.

The head turning, the vomit, the spider walking, that was all shocking (and cool) but not scary.

What I did find scary was all the science/medicine stuff. Doctors telling the mother that Reagan is faking it, or keeping her under sedation, or subjecting her to endless invasive tests. The real horror is the mother's realization that the material world cannot save her daughter. The horror of putting Reagan's life in the hands of faith.

So I'd say that it works on several levels, where for some people, scary is "OMG, a monster face!" and for others scary is the incomprehensible.

https://www.rottentomatoes.com/m/hausu

And a scary movie is a hunting movie seen from the POV of the prey.

Horror is a meme of a genre.

But actually I like "scary movies" not because "scary" but because "Monsters, Magick, Aliens, Kaiju, and Slashers are fun." Simply gore, torture porn, or jump scares just don't do it for me, I need an element of whimsy. I'll take Leprechaun in the Hood, or Jason X, or Killer Clowns from Outer Space, or The Thing, or Godzilla Vs Biolante, or The Blob, or even Attack of the Killer Tomatoes and Maximum Overdrive, before Hostel or Saw.

Just like any other film, what it actually needs is good writing, good acting, and good cinematography, parts which are more concrete than whether something's scary. The horror part is essentially just an aesthetic which a movie can sit within.

Also, quite often the view that 'scary movies should be scary' just leads to directors creating films that are hard to watch, period - full of vapid jumpscares, scenes made to just gross out the audience, and often just torture fetish content. It's a terrible metric to aspire to that generally degrades the entire genre imo.

Ding dong. You're dead.

Even has a great subtitle