Because reflowing 1000 words is a lot simpler that designing a general method for conveying your message on any given aspect ratio, resolution and size.
Because text is a lot more portable across platforms.
Because interacting with text is a lot easier to automate. And extracting information from text automatically is easy whilst extracting it automatically from a picture is very difficult.
GUIs are great for discoverability, and complex long ineractive sessions. But they also have downsides.
Why use a picture when you can tell the computer what to do, such as going out to the café while the computer is either number crunching/photo editing with ImageMagick by itself?
