My main problem, and the reason I didn't finish the series was their advance was very low and the royalty rate was too. After looking round it seemed the rate was probably reasonable for authors in other fields, but very bad compared to what I would earn actually programming. Plus they absolutely refused to give me any indication of how many sales I could expect. I couldn't justify spending the time to complete the series vs regular contracting. I think this low remuneration affects the quality of the authors they are able to attract, so you're right in that part.