I think an element of being scared is surprise and the unknown.

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.