I think you might have missed an element. For the book example, I made an edit to my post that tries to clear that up: it's not about selling it for someone else to consume, it's more about selling it to multiple publishing systems. As on Steemit, you do not pay to read a post in the same way you would pay to read a book. For software development, you don't sell the print function you use to someone else, you sell whatever product you built, and that may include open source libraries, but the open source libraries are not what you're selling: you're selling the specific pieces that you wrote.