From what I can tell in the author/publishing world, a lot of this is a decision of what markets the publisher specializes in.
Baen is offering _Sheepfarmer's Daughter_ free (this is always done with the author's full participation) and reissuing the Paks series--this means more sales for Moon through Baen. Other authors, like Bujold, work with Baen and other publishers as well. But if Moon is going artistically in a new direction that Baen doesn't specialize in, then it makes sense for her to seek out a new publisher that is more likely to accept and appropriately market her new books.
Also they could pay more
At any rate you're not
forced to pirate her books. Libraries tend to stock them, as do bookstores specializing in print products.