Many CMS's are designed by developers, for developers. Building and maintaining a site with them can be pretty complex and intimidating for someone who can't program computers (Which ironically, is most of us!). The end editing experience works, but to make even basic content changes you're typically working with long web forms in a "back-end." Imagine having to call a consultant every time you wanted to write a new Word document. How useful is that to your business?
Conversely, there's a number of solutions that are geared for the DIY market. Typically starting as a blog, these sites get added to and added to over time until they fall apart. Imagine being told your document was always going to have a cover page, a table of contents, and an index – no matter how simple you wanted it to be. Sure it's great you can get started quickly, but if you want to do much more than what these systems were designed for like using a hammer to drive screws.