More and more, the internet is turning into a place where people want content. When people visit a website, they want to see high quality organic content on that site that they can actually learn something from. As such, more and more businesses are turning to high quality article writers to write quality articles.
Some sites actually buy articles from other sites. Freelance writers sometimes write articles and then sell them to different websites. Freelance writers are not employed by any one company, but once they sell the articles, they typically no longer own the rights to said articles.