 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. If you have access to a work for reading but want to translate it into another language, distribute copies to colleagues, copy the text for mining with sophisticated software, or reformat it for reading with new technology, then you generally need the permission of the copyright holder. 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. Second, academics have salaries from universities, freeing them to dive deeply into their research topics and publish specialized articles without market appeal. As incentives for productivity, these intangible career benefits may be stronger for the average researcher than royalties are for the average novelist or musician. There’s no sense in which research would be more free, efficient, or effective if academics took a more “businesslike” position, behaved more like musicians and moviemakers, abandoned their insulation from the market, and tied their income to the popularity of their ideas. Nonacademics who urge academics to come to their senses and demand royalties even for journal articles may be more naive about nonprofit research than academics are about for-profit business. Scholars can afford to ignore sales because they have salaries and research grants to take the place of royalties.
 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.