I just didn't get it was because it was outside my price range for a D&D product.
I think there were several reasons people didn't pick up this product.
First, it had a narrow focus.
Second, as you mentioned, the price was pretty hefty for such a focused item (not that the contents weren't worth it for those who wanted to shell out the bucks).
Third, the early releases were delayed due to bad cards.
Fourth, some of those bad card sets showed up on Amazon even after they were supposed to be replaced, which led to large returns and horrible Amazon reviews. If I recall, Amazon at the time showed an average reviewer rating score of between 1.0 and 1.5. The reviews got much better after the sets with good cards were stocked and are now averaging a 4.6 rating.
Fifth, the big box bookstores didn't stock this product, or at least they didn't get it into the stores at the time it was released, and they also didn't list it in their online catalogs. I'm specifically referring to Barnes & Noble and Books-A-Million since those are the stores within my driving distance. They list it in their online catalogs now, but didn't then. This happened at the time WotC changed their distribution network, dropping Penguin Random House, so I figure that's probably why the big bookstores weren't able to initially get any stock. So, folks without a FLGS in their area were hard-pressed to get a copy at time of release.
Bottom line . . . For all the above reasons, probably not many people purchased this item when it was originally released which would lead to few postings before interest had cooled.