Three reasons why:
1) Pacing. Most TV shows for which each episode is part of an extended story arc pace themselves out. You see the egg in the first episode. The skillet in the second. The burner comes on in episode three. By episode six or seven, someone is eating scrambled eggs. In AHS someone mentions eggs, and seconds later someone is cracking one open against his forehead and swallowing the raw yolk whole (not an actual scene from the show; a metaphor).
The show operates in 12-episode chapters; season one told a story; season two features many of the same actors but in entirely different roles and settings. When, no matter how well the audience receives your story, you only have 12 episodes to work with, it means you have nothing to lose. AHS comes at us with the urgency of a short story, not a novel, with absolutely no fear of about emotionally or physically eviscerating major characters (worst case scenario, they can always come back as ghosts). It’s television without fear, about fear.
2) Human Horror > Monster Horror. To date, AHS has included in its cast of characters ghosts, monsters and aliens. While the supernatural creatures allow for atmospherics, plot twists, and wonderful subversions of the viewer’s expectations, they ultimately amount to sizzle; human nature is the steak. The first season’s haunted house story was themed around infidelity; most prominently the aftermath of an extramarital affair, but more broadly betrayal of family, values, and even oneself. Season two, set in an asylum, seems concerned with different forms of perfidiousness: hypocrisy; selling out the ones we love or our ideals for the sake of our own self-preservation.
Note the choice of words: our, not their; self-preservation, not self-betterment. The characters are all too real, and the best of them rarely make choices any rational person, in the same distorted situation, wouldn’t agree to (or at least strongly consider). These characters are out of luck, conflicted, and make choices that don’t just make the plot move, but seem necessary for their very survival. We relate to them because, at our worst, we are them. That’s horrible, terrifying, and beautiful.
3) Indulging our worst instincts. This has to do with both pacing and human horror. AHS sets us up to have preconceptions, and has a tendency to do one of two things from there: undermine the expectations gradually, or deliver on them with shocking rapidity.
SPOILER ALERT—IF YOU HAVEN’T BEEN WATCHING SEASON TWO AND INTEND TO, DON’T READ THE NEXT TWO PARAGRAPHS
We see a corrupt woman running a corrupt asylum. We see a reporter out to reveal her to the world. We see a man who ostensibly does not belong in the asylum getting all-but-tortured. We see the reporter wander the darkened halls of the asylum when she’s not supposed to be there. We realize that, if the reporter isn’t careful, she could find herself wrongly imprisoned and subject to the same horrors. We pat ourselves on our backs, because we think we might have foreseen a major story development that could come up later in the show and grow drunk on the potential.
Then the reporter gets caught. The next time we see her, she wears institutional garb and is strapped down to an examination table. Our worst fears and greatest hopes for the season have been realized in a matter of minutes. And the season premiere still hasn’t even finished yet.
AHS can be gratuitously gory and sexual, particularly for a free TV show. It’s not for everyone. But if you have the stomach to get past all of that (or if all of that is your cup of tea) there’s no richer hour of television going today.