I can’t speak to why they were chosen, but I can tell you that we’ve been using the Greenleaf Famous Men books for years (we started before Memoria Press was publishing them) and we’ve always been very happy with the quality of the Greenleaf books. From doing some reading about the differences, I have read reviews that say that the Greenleaf books are more “living book” style rather than workbook style. I didn’t see any reason to reinvent the wheel (or spend more money) and replace the books I had already invested in, so we’re sticking to Greenleaf. I’m also very grateful to the Shearers for re-publishing the books in the first place and making them more accessible to homeschoolers, so I like that they get some profit from my purchases.