From what I've been told, Central has been in regular contact with Avon about any feasible TSB project you could imagine (including a new hardcover edition). Avon's current management just isn't interested in doing a major Satanic book release at this time, for various reasons. I'm sure one day they will come around and we will all be delighted to purchase such an edition at that time, but until then (as you know) the paperback is readily available.
This is kind of a cheeky question, actually. It has to do with business relationships and ongoing negotiations, and there's no real reason why Central would feel compelled to explain further in public. Think about it.