There's a simple reason why horror games are less prevalent.
Horror builds as the story ends. In a game we expect, nay demand, a building hero who defeats the bad guy - and the few horror games that have been done - Space Gun, Beast Busters, Darkseed all use either: the ticking clock to death, the big twist reveal or the "it was only the baby/scout, here's the mother"; and then end.
In a good horror, you need to be isolated, alone and scared - while sitting on Steam/PSN/Xbox live, in a bright room drinking beer. The two areas aren't really conducive.
And if you up the stakes, "This time your save file is on the line", people will go nuts because "THIS ISN'T WHAT I PAID FOR."
Either way, you'll lose trying to write a horror game.
So, don't write a horror game : Instead write I Wanna Be The Guy, Alien Versus Predator, MarioKart and all those other games that horrify rather than terrify. Because even John Carpenter can tell you stories of the "one hit kill that you ALWAYS know is coming".
Horror can't be scary unless it attacks the fundamentals of what you trust. A horror game has to be break one rule, but keep to all the rest - and that's pretty tough to do.