Old things are scary. I once visited a retirement facility (which is the new, cold way of saying "Old Folks Home!") when I was young, where a woman who I am pretty sure had no eyes said unintelligible things to me in a raspy voice. I once owned a car from 1985 that was totaled when a tire blew up, causing the vehicle to flip over. Abandoned houses are a favorite spot to visit on Halloween just so I can get cheap thrills.
Similar to all of the old things that have scared me are old pieces of film. Old horror movies (and I mean old) can scare me just on the principle of being old. There is something very creepy about the lavishly built sets of giant mansions, seen only through limited camera angles (rather than a million computer rendered ones) that is surreal. Huge staircases that simply sit, imposing, gray and black with white light reflecting off of them, all on a silver screen, seems ethereal and terrifying.
Proof that old things scare me just because they are old is Jack Clayton's 1961 The Innocents. I did not like Henry James's 1898 The Turn of the Screw because the story was kind of uneventful, and the suspense did not seem to build up well. Put those same scenes of a woman (Deborah Kerr) wandering around a mansion looking for creepy kids, Miles (Martin Stephens) and Flora (Pamela Franklin), into a movie done on the silver screen, and I shall be looking over my shoulder for weeks!
Maybe it is the resolution in old films that makes them terrifying. A lot of details are lost when one sees a film in monochromatic grays. Every character, every location, every item seems less real when done in black and white. Similarly, sound technology was more primitive, and sound effects are more obviously superimposed, again separating the story from reality. This illusion of watching people in a place other than reality is the clincher.
After watching an old horror film, I have seen, with my own eyes, a young woman, pale with long straight black hair, staring lifelessly towards me. The camera zooms in on her, or away from her, in a way I have trouble conceptualizing on my own because of modern effects. There are real people in old films, but they are presented in a way that distorts reality. This brings about the conflict of knowing that I could see real people like them in real life, but not in the way I saw them on that screen. Trying to imagine the ghosts from The Innocents walking through my house gives me nightmares.
I am not sure how scary these movies would have been if I had seen them when they were released. Old movies, when they were young, were just movies. I can argue that they would still be separate from reality, but CGI separates me from reality in an equal, yet different way, and I am just not scared by modern horror. This leads me to believe that the limitations set by old film technology forces the stories to be told in just the right way--with just the right amount of separation from what I can easily imagine--to scare me more than I enjoy, but enough to keep me coming back.