Well, y'know, publishers have overhead. They have to include the cost of all that drive space they'll need to store the ebooks. And the cost per book it'll take to train random office workers on Sigil, and the additional retraining fee to teach one of 'em to use Calibre 'cos the computer with Sigil installed isn't working today and their firewall has all the free download sites blocked.

(I can understand "converting to ebook formats takes some training & formatting time." I'm not buying that it takes more time than formatting for print, even with the fact that most places have given up on manual kerning and widow/orphan control.)