Basically, what Oscarvarium said. But let me add some specifics. Contrary to popular belief, RBN isn't always a no-risk proposition. We've talked with bands who would have to spend over $1,000 just to get the isolated stems and get them into a RBN-suitable format. When, as a band, you're making 25 cents on the dollar (at most) for RBN downloads, and only getting 500-1000 downloads (if you're lucky), you really can't justify those costs from a purely financial standpoint.
But... don't TAG already have the Ascension stems? There was a preview video release a while back and stuff