That's part of the problem. They're aiming low and hitting even lower. Not all fans of a certain show who would want DVDs of said show read these "niche magazines". I don't mean to imply that every studio should go and take out a full-page ad on the front page of the New York Times. They need to spread these things out beyond the niches.
They've been playing it safe for far too long and the sales reflect (partly) those results.