Backlinks are as old as the Internet. In fact, you can argue that backlinks are the foundation of the Internet. Outbound links hold the Internet together.
The algorithms of search engines have always relied heavily on the existence of backlinks. For a long time, backlinks were by far the most important ranking factor. And some SEO’s think that links are still the number one ranking factor to focus on.
As such, it’s no surprise that backlinks have turned into a commodity. They are valuable, they cost money, they can be sold, they can be bought. And because they are so important and valuable, a lot of bloggers and Internet marketers are hesitant to include outbound, external links in their content.