There are also traditional publishers that are cutting hybrid deals, in which authors pay for some services in exchange for higher royalties. (publetariat.com)
But perhaps the best reason is because authors publishing under «higher» packages earn higher royalties and their book copy prices are less expensive. (brentsampson.com)
Sometimes there isn't a whole lot of difference in the cost and if authors get higher royalties from one form over the other, then there is the impetus to purchase that format. (jimchines.com)