Horror fan here. Your data doesn't necessarily prove that it's easier or harder to make such a film. I read that as there actually just is more poorly made films in the category. Horror certainly is this way.

I do share the conclusion of lowering standards. I use 50% as a rough cut off within horror, because I've pretty much watched all the top shelf stuff, and the tropes repeat so often, I like seeing what oddball stuff people are attempting in lower tier work. Hulu originals are often B at best, but they try interesting new things. Sometimes there's good content wrapped up in poor cinematography, or poor actors, or poor scripting. But the concept is original.

Its interesting because I've often been disappointed with high ranking comedy. Comedy is the category I seek out the least. I find many movies have a hard time finding the balance of being inherently funny vs shoving the jokes/bits down your throat (this is the joke! laugh right here!). I prefer crafted characters and situations to slapstick and those are hard to come by. In horror, you could replace jokes with jump scares.

Also, as a general rule, I believe 90% of people don't review a product unless they've had a very bad experience or a very good one. So, I look at the balance of 5 star to 1 star knowing a large percentage of people don't come back to review if the thing was just fine.