Part of what makes the question challenging is that I certainly don't like all or even most of them. There are various subgenres within horror that I don't care for at all even though there are usually exceptions. For example, I don't usually like films that are sometimes described as "torture porn," but there have been a handful of these films that I have found worthwhile (e.g., Audition). I mention this because the reasons I like one horror subgenre might have little to do with why I like another. For some genres, the appeal is mostly the special effects or even the cinematography; for others, it is far more about the plot and character development. It makes it tough to answer the question in a general sense, but I'll try to do so anyway.
Why do I like horror films? I think the best way to approach the question is to consider what I look for in a horror film and what characteristics are shared by my favorites. In other words, what makes a horror film great rather than just good? The great ones are genuinely scary and/or disturbing. To be great, I must be affected by the film. I don't watch horror because I'm looking for a laugh; I watch them because I want to be scared and/or disturbed. I want to find myself thinking about it the next day. I recognize that others may be looking for different things, but that is what I'm looking for.
My favorite horror films have some things in common:
- Creepy atmosphere. I have certainly enjoyed horror films that did not deliver here, but most of my favorites are noteworthy for effectively creating a creepy atmosphere that keeps the audience unsettled through much of the film (e.g., Session 9). There are a few films that I watch over and over again even though I don't particularly care for them just because of the atmosphere they created in a few key scenes (e.g., An American Werewolf in London).
- Effective character development. This is where most horror films fail, and nothing ruins one for me like the lack of characters I care about. When I don't care about the characters or find them annoying, there is no possibility of fear. I can still sometimes enjoy such a film, but I have to do so for other reasons (e.g., special effects in the kill scenes).
- Supernatural elements. Many of my favorites involve some aspect of the supernatural. While I tend to find those that do not far more disturbing (e.g., Eden Lake) and enjoy many of them, I usually prefer those with at least some hint of the supernatural.
- Emotional impact. My favorites are memorable in the sense that they make the sort of emotional impact that leads me to think about them the next day. Two of my all-time favorites, Poltergeist and A Nightmare on Elm Street, scared me so thoroughly when I first saw them as a child that they still have the capacity to transport me back in time when I watch them today.
- Art. Even if a film fails on to deliver on most of the points above, I can often appreciate it if it delivers on the art. Many of Argento's films fall into this category for me. I absolutely adore Suspiria as a work of art despite its flaws. I seem to appreciate it more every time I see it.
Back to the original question. Why do I like horror films? I like different films for different reasons, but I think I can identify a few things that apply in most cases:
- I like horror films for their ability to evoke strong emotions (ideally fear) without actually placing myself at risk. They make me feel something that other genres rarely do, and this is the main attraction.
- I appreciate the art involved in many of them (e.g., writing, special effects, cinematography), including those that don't necessarily deliver on the first point.
- I find their relatively low cost appealing, as they allow new filmmakers to break into film-making easier than many other genres do. I love to see what new filmmakers can accomplish on small budgets.
- I find that horror is one of the few genres where I can actually enjoy bad films. That is, it can be fun to watch horror films that fail miserably in what should be the shared goal of all horror (i.e., to be scary or disturbing in some manner).