Too many good reasons here.
1) With homoginization of the airwaves by broadcast conglomerates, many good artists don't get airtime.
This also affects all music sales in general, however, and is not limited to LP sales.
The way to hear new music that's not what is what the music business is pushing for maximum profit and easy marketing efforts for them?
Typically word of mouth, music blogs, college radio or internet radio, live shows, eclectic friends, and by accident.
Pandora, perhaps the greatest thing to happen to music sales in regards to radio/internet airplay, was quickly saddled by the RIAA, and now is mired with commercials and consumer-oriented fees.
2) Just want that old time rock and roll. New music just isn't all that great.
Oh boy- there's some fantastic new music out there! But we just get limited to no exposure to it. See above.
3)Its the economy...
A big part of it, I imagine.
Let me also add a few more-
1) Novelty.
Records are, to many, a novelty. A hip trend. A few may become converts, but with all the Crosley and Ion tables out there being sold, many may lose interest as they never hear true high fidelity.
Sure, they hear better music reproduction than what an overly-compressed MP3 sounds like, but nothing what a true hifi setup offers.
2)Frustration vs. convenience.
LP playback is a commitment. An effort. And doing things the hard way isn't charming to everyone, despite the dividends and high-quality payoff.
3) Sloppy pressings and high prices.
While this doesn't apply to all new re-issues and new pressings, plenty of new records are poorly pressed and priced very high. How many times does one want to shell out $30-$50 for a fancy glossy record only to have it pressed off-center, covered in fingerprints (and in my case human hair), scuffed and scratched, or just poorly mastered?
My thoughts on the topic.