Not that it changes your overall point, but they didn't. They sold away the rights before they spent the two and a half years writing their book. If they hadn't

Not that it changes your overall point, but they didn't. They sold away the rights before they spent the two and a half years writing their book. If they hadn't gotten the advance and therefore the ~guarantee it would get published, they might not have written it in the first place. But they can't choose to self-publish after they finish it, because they chose to sign their contract long before that.