As I writer I know well the devaluation of our trade, especially with online content farms. It used to be that all texts were paid based on quality and intended use, such as for a print magazine and so on. Now, everyone pays by the word, and most people now expect to get content for $2 or less for a full article, because regardless how low they pay, someone out there will accept to write. I guess on the case of Medium, make the site look nice enough and people write for free.