When you read horror, do you like them to be short stories or novels, and why? For me, I prefer short stories. While there are plenty of horror novels that I've enjoyed, none of them actually scare me. Short stories will hut you with the scary stuff and wrap things up before it overstays its welcome, like a scary ding dong ditch. The longer a story stretches itself out, the less scared I am, usually.
I definitely see your point—horror is harder to sustain for the long haul. I've probably read a lot more horror shorts than novels, but I'd say it depends on how well it's done. If the author is able to sustain it long term then cool. And that probably has a lot to do with how it's handled. If it's really intense and unrealistic, then probably keep it short. But if it's done more like a Stephen King (when he was at the top of his form) then a novel is fine. Though usually the actual horror elements of his stories tended to be bizarre and not that great when revealed, he was able to write long stories focusing on character, and to go into great depth about the various characters and the way their stories interconnected. I also enjoyed the Southern Reach trilogy of novels much more recently. Very bizarre and quite literally weird, but again for much of the time the focus was on characters in at least somewhat 'normal' settings with mostly just the shadow of weird horror lurking. Plus the weird stuff was fascinating, and that goes a long way.
For me, it's about what else is in the story. Personally, 'pure' horror tends to lose its charm fairly quickly, no matter how interesting it starts, but if it's wrapped around a compelling mystery and character development, then the other elements hook me with the horror adding stakes and flavor and keeping tensions high.
Do I like long stories or short stories? Yes. I think what the OP raises is a peculiarity of horror writing - the scary bits are so stylized and technical that there's a choice between polishing and pruning them to stand alone, or using them to pepper a longer story with lots of other things going on. At the worst extreme, a unique or mindblowing concept (be it gross, or macabre, or sinister, or just squicky) is stretched and stretched and stretched... until it fills one of those paving-slab sized tomes that people read on trains. And the cunning and technically-beautiful core of the story might only emerge again years later when they adapt it into a film. "Oh, this is mysteriously better than the book since we've abridged it." And sometimes that happens repeatedly with the same author. But like all speculative fiction - a good horror novel isn't about its scary bits. Good sci fi isn't about the science. And good fantasy isn't about the fantasy. Good novels are about characters. And the horror elements should be seen as a way of pressuring and revealing characters - in ways that couldn't be done in other genres of fiction. Character is vital to shorts as well - but the long-form novel is the higher art form. The depth and investment a novel can give us in the characters should always be able to raise the stakes above a horror short. A character we don't love being chased by a technically-impressively-unpleasant new bogey - versus - a character we have come to trust being chased by a bog-standard zombie. Assuming it's executed and polished to the same standard as a short (which isn't a given), the latter wins - and it's also more flexible because a huge spectrum of situations that wouldn't qualify as horror per se can become frightening to us just because of that investment in and attachment to the character. And there's nothing stopping novelists from using horror scenes outside of the genre - so long as it fits the story. I can't think of many examples or good ones now but 'The Road' is scarier than many horror novels. Maybe horror's best when it isn't in a short horror story or a long horror novel at all, but springs out unexpectedly from a book you thought was about a man going for a walk.
Okay. . .boy, do you get horror. Somehow, you pinpointed exactly what has caused me to be working on my first novel. . .at 64. Thank you for making me realize I'm not crazy!
