When you are watching a silent film, much of the narrative is transmitted through title cards (the original text messages). Yes, action is happening, but often the context of the action is unclear until the title cards explicate it. Some silent films don't have many title cards, so the action can persist for quite a while without explicit explanation. In the case of a silent horror film--the almost silent Vampyr, for example--the mood can build and build as you await the next title card, the next slice of dialogue, to interrupt the momentum of gloom. And as time passes, every movement on screen becomes part of a slow burning, dream-like anxiety; where every dart of the eyes and every cautious step forward seems to have tremendous import. You forget that it's just a scene with a guy walking through a field.
What it comes down to is misdirection. In a talkie horror, with the constant dialogue (and with it, explanation), things are much more on the surface*. The advantage of misdirection that you find in silent horror films can also be found in effective horror novels. There are all kinds of distractions; minor characters, minor character details, location details. These distractions help magnify the story's ending because you're diverted by all the dead-ends and false starts leading up to the ending and therefore less likely to see it coming.
When you read horror short stories, there is less room for misdirective details, so the ending and direction of the plot is easier to guess. Same goes for horror anthology TV shows like "Tales From the Darkside". Because of time constraints, the expositions are necessarily abrupt. The dialogue must come right out and announce what is happening. There are no extraneous details to obscure things, so you fixate purely on the story. And let's face it, it can only end a few different ways. And because the story is so predictably compressed, you know that after that last commercial break, it has to end somehow. And if you have seen a few horror anthology episodes, you can pretty much guess the ending to all of them.
I think these mechanics partly explain why there are so few decent (let alone great) horror films, and why there are so few horror anthology episodes that are even worth watching all the way through. There is a reason why every classic horror film list pretty much has the same handful of titles on it...not that many classics to choose from.
*The Blair Witch Project and the Bela Lugosi Dracula are two talkies with creepy, silent film-like pacing. Many early talkies of all genres were short on dialogue as the medium made the transition out of the silent age. {Via}