Most classroom teachers in the U.S. don’t need to sell because they are either employed at public schools (attendance is compulsory), or at private schools (selling is handled by the school administration).
In the long run, online learning will probably become dominated by the equivalent of private schools: companies that hire great teachers and, separately, great marketers to build audiences.
Or look it at this way: Nonprofit authors don’t generally design their own book covers. They work with a publisher who does that. Why should teachers try to design their own YouTube thumbnails?
(On the flip side, if you highly value your independence as a sole proprietor, then yeah, expect that you’ll have to put on the marketing hat sometimes).