It’s a tiny card, likely with low yields from the manufacturing plant. The manufacturing process is in its infancy for these larger cards, and reaching this point was likely a struggle (else, we’d have had 256 GB instead). Why would they price a card this capacious at a point where they would have to eat the costs of development? And why would they price it so low that they ended up completely selling out of limits batches of early stock? Never mind that they probably expect this to be a low volume part for quite some time, compared to cards in the 8 to 32 GB range.
Like every technology, prices will come down after some manufacturing optimizations, after demand is shown to be high enough (and sustainable), and after other companies catch up.