The major reason they don't work, IMHO, is because many creators simply don't know about them, don't understand them, and don't understand the general point, leaving it to their lawyers to deal with stuff and thus going contrary to what they would otherwise believe.
Then you have people like Seth Godin. He published an 100+ ebook and put it out under Creative Commons.
Then someone went and published it as a paper book.
He wasn't exactly happy about it.