One of the biggest problems with recent horror movies--indeed with most genre fiction these days--is that they are being made with idea of "franchise" foremost in mind. This is at the core of the recent spat of remakes that have been plaguing our theaters. Hollywood doesn't want a good scary movie...they want a brand name. They want a Freddie or a Jason or a Michael Myers. Sure most of the classic great horror flicks spawned sequels...but they were more of the "Hey that did well, let's make another one" variety rather than the planned as a series from the beginning variety.
I've seen some good horror movies over the last decade (glancing at my DVD shelf I can pick out Dead End
with Ray Wise and May
with Angela Bettis) but they don't end up getting any real studio support...they get a tiny theatrical release (if they're lucky) and get thrown onto video where their audience consists mainly of people who are already inclined to seek out those kind of movies. The general public never even gets to see them and so they never get a chance to become "important".