 How could selling their work actually harm some authors' interests?
Authors who share their works in this way aren’t selling them, and even authors with purposes higher than money depend on sales to make a living. Suppose that selling their work would actually harm their interests by shrinking their audience, reducing their impact, and distorting their professional goals by steering them toward popular topics and away from the specialized questions on which they are experts. Copyright can also be a significant access barrier. Even these authors, however, tend to transfer their copyrights to intermediaries—publishers—who want to sell their work. In addition, replacing user freedom with permission-seeking harms research authors by limiting the usefulness of their work, harms research readers by limiting the uses they may make of works even when they have access, and thereby harms research from both directions. Second, scholarly journals generally don’t pay authors for their research articles, which frees this special tribe of authors to consent to OA without losing revenue. This fact distinguishes scholars decisively from musicians and moviemakers, and even from most other kinds of authors. The academic custom to write research articles for impact rather than money may be a lucky accident that could have been otherwise. But it removes a major distraction by allowing them, if they wish, to focus on what is likely to be true rather than what is likely to sell. Creative people who live by royalties, such as novelists, musicians, and moviemakers, may consider this scholarly tradition a burden and sacrifice for scholars.
 The cost to read the work could result in a smaller audience.
 It could steer them toward writing about popular topics rather than writing about their expertise.  Libraries may decide not to purchase the work because of the cost involved for multiple copies.  They may never reach a global audience.  The cost to read the work could result in a smaller audience.