It feels like a generational thing, too. My aunt and uncle showed me the 1932 production of "The Mummy," and it terrified them. They were born in the 40s, and so saw this movie in their teens. (and perhaps even later) I watched it recently, and can't even imagine being scared.
I'd like to think that there is both an objective and subjective aspect to this. On the one hand, maybe people just can't appreciate the older styles of art. On the other hand, after being exposed to modern violence, cinematography, and suspense, the old techniques truly do pale in comparison, at least in the visceral, emotional sense.
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).
Granted, I was a teen in the 90s, but I never found Doom to be scary. However, Wolfenstein 3D left me an anxious wreck -- likely because the AI always (seemed to?) know where you were. (I also didn't get to play Wolf3d until DOOM had already come out, so I don't think it's related.)
>That is the 100% the core idea of Doom lore.
That was created specifically in 2016 Doom. Prior to that, Doom didn't really have much of a story.