I wonder how much of the difference is attributable to sensitivity (or lack thereof) to the art/medium/representation, and how much is due to the fact that the fears addressed by the work of art were more relatable to people at the time than they are to a modern audience.
My mom found "The Exorcist" truly frightening, so much so that she refused to re-watch it in adulthood. So my friend and I rented it one night looking forward to a good scare; instead, we mostly found ourselves laughing at how ridiculous it seemed. We must have been around 12 at the time, so probably already quite desensitized to horror movies in general, but I think it is also the case that the subject matter was just less frightening to us than it was to her. We were all raised Catholic, but she was of the stern-nuns-with-rulers generation whereas our elementary school in the 90's had been of the hippie-nuns-with-guitars variety. I don't think things like demons/the devil had ever felt like real objects of fear for us like they may have been for her (in such a deep way that their representation continued to creep her out long after she stopped believing in their literal existence).
My mom found "The Exorcist" truly frightening, so much so that she refused to re-watch it in adulthood. So my friend and I rented it one night looking forward to a good scare; instead, we mostly found ourselves laughing at how ridiculous it seemed. We must have been around 12 at the time, so probably already quite desensitized to horror movies in general, but I think it is also the case that the subject matter was just less frightening to us than it was to her. We were all raised Catholic, but she was of the stern-nuns-with-rulers generation whereas our elementary school in the 90's had been of the hippie-nuns-with-guitars variety. I don't think things like demons/the devil had ever felt like real objects of fear for us like they may have been for her (in such a deep way that their representation continued to creep her out long after she stopped believing in their literal existence).